## WBBSE Class 9 Physical Science MCQ Questions Chapter 3 Matter: Structure and Properties

Well structured WBBSE Class 9 Physical Science MCQ Questions Chapter 3 Matter: Structure and Properties can serve as a valuable review tool before exams.

## Matter: Structure and Properties Class 9 WBBSE MCQ Questions

Multiple Choice Questions :

Question 1.
atmospheric pressure is measured by :
(i) hygrometer
(ii) pyrometer
(iii) Barometer
(iv) spherometer
Barometer

Question 2.
Construction of a submarine is based on :
(i) Archimedes’ principle
(ii) Bernoulli’s theorem
(iii) Pascal’s law
(iv) Boyle’s law
Archimedes’ principle

Question 3.
Why is the dam of water reservoir is thick at the bottom?
(i) quantity of water increases with depth
(ii) density of water increases with depth
(iii) pressure of water increases with depth.
(iv) temperature of water increases with depth.
The pressure of water increases with depth.

Question 4.
A wooden block is taken to the bottom of a deep, calm lake and then released. it rises up with a :
(i) constant acceleration
(ii) decreasing acceleration
(iii) constant velocity
(iv) decreasing velocity
Constant acceleration

Question 5.
A capillary tube made of glass is dipped into mercury. Then
(i) mercury rises in the capillary tube
(ii) mercury falls in the capillary tube
(iii) mercury rises and flows out of capillary tube
(iv) mercury neither rises nor falls in the capillary tube
Mercury falls in the capillary tube

Question 6.
If the diameter of a capillary tube be doubled then the height of the liquid that will rise is :
(i) twice
(ii) half
(iii) same as earlier
(iv) none of these.
Half

Question 7.
Two pieces of glass plates one upon the other with a little water in between them cannot be separated easily because of :
(i) inertia
(ii) pressure
(iii) surface tension
(iv) viscosity
Surface tension

Question 8.
There is dip in the capillary tube when the angle of contact θ is :
(i) θ = 90°
(ii) θ = 0°
(iii) θ > 90°
(iv) θ < 90° but not zero
θ < 90° but not zero

Question 9.
The rise of liquid in a capillary tube has a meniscus. If the angle of contact be 90°, the shape of the meniscus is :
(i) concave
(ii) convex
(iii) flat
(iv) none of the above
Flat

Question 10.
In Bernoulli’s theorem, which of the following is conserved ?
(i) mass
(ii) linear momentum
(iii) energy
(iv) angular momentum
Energy

Question 11.
The gale blows over a house. The force due to gale on the roof is :
(i) in the direction downward
(ii) in direction upward
(iii) zero
(iv) in the horizontal direction.
In direction upward

Question 12.
To calculate the flow of a liquid, which of the following is used?
(i) Stoke’s law
(ii) Bernoulli’s theorem
(iii) Poiseuille’s law
(iv) Conservation of pressure
Poiseuille’s law

Question 13.
Scent sprayer is based on :
(i) Charles’s law
(ii) Archimedes’ principle
(iii) Boyle’s law
(iv) Bernoulli’s theorem.
Bernoulli’s theorem

Question 14.
In old age arteries carrying blood in the human body become narrow resulting in an increase in the blood pressure. This follows from
(i) Pascal’s law
(ii) Stoke’s law
(iii) Bernoullis’ principle
(iv) Archimede’s principle
Bernoulli’s principle

Question 15.
On which of the following the terminal velocity of a solid ball in a viscous fluid is independent?
(i) area of cross-section
(ii) height of the liquid
(iii) density of the both
(iv) density of the liquid
Height of the liquid

Question 16.
A body of weight mg is hanging on a strain, which extends its length by 1. The work done in extending the string is :
(i) mgl
(ii) mgl / 2
(iii) 2 mgl
(iv) none of these
mgl / 2

Question 17.
According to Hooke’s law of elasticity, if stress is increased the ratio of stress to strain :
(i) increases
(ii) decreases
(iii) becomes zero
(iv) remains constant
Remains constant

Question 18.
S.I. unit of pressure is
(i) pascal
(ii) Kgfm-2
(iii) atmosphere
(iv) none of these
pascal

Question 19.
upthrust depends upon –
(i) volume
(ii) density
(iii) g
(iv) all of these
all of these

Question 20.
If the density of the object placed in a liquid to the density of the liquid, the object will –
(i) float wholly immersed
(ii) float half immersed
(iii) sink
(iv) float completely above the liquid
float wholly immersed

Question 21.
Atmospheric pressure is measured by –
(i) hydrometer
(ii) barometer
(iii) sonometer
(iv) ammeter
barometer.

Question 22.
Relative density s of a substance is related to the density of the substance ρ and density of water at 40C d as –
(i) s = ρ × d
(ii) $$\mathrm{s}=\frac{d}{\rho}$$
(iii) $$\frac{\rho}{d}$$
(iv) $$\frac{1}{\rho d}$$
$$\frac{\rho}{d}$$

Question 23.
SI unit of surface tension is
(i) Nm
(ii) kgfm-1
(iii) mN-1
(iv) Nm-1
Nm-1

Question 24.
The terminal velocity of a spherical body depends on
(ii) density of the medium
(iii) viscosity of the medium
(iv) all of these
all of these

Question 25.
Bernoulli’s theorem is based on conservation of –
(i) mass
(ii) mass and energy
(iii) energy
(iv) none of these
energy.

Question 26.
With increase in temperature, the elasticity of a material
(i) increases
(ii) decreases
(iii) remains unchanged
(iv) nothing can be said
decreases

Question 27.
The solids if break soon after crossing elastic limit are called
(i) ductile
(ii) brittle
(iii) malleable
(iv) plastic
brittle

Fill in the blanks :

1. The word fluid comes from a Latin word _______.
Fluere (meaning ‘to flow’)

2. The branch of physics which deals with fluid at rest is called _______.
Hydrostatics

3. The branch of physics which deals with fluid in motion is called _______.
Hydrodynamics

4. Specific gravity of a substance is the ratio of the density of a substance to the density of _______ at 4°C.
Water

5. In CGS system, the density of a substance is numerically _____ its specific gravity.
Equal

6. The unit of pressure in SI is ______.
Pascal (Nm-2)

7. The liquid pressure is a ______ quantity.
Scalar

8. Archimede’s principle does not hold when the body is in ______ condition.
Weightless

9. When the weight of the body is greater than the weight of the liquid displaced, then the body ______.
Sinks

10. Condition of floatation of a body is such, that the weight of the floating body must be ______ to the weight of the liquid dispiaced.
Equal

11. If the density of the body be equal to the density of the liquid, the body ______ completely immersed any where in the liquid.
Floats

12. The height of a water barometer is ______.
10.33 m

13. The forces between the molecules of substances are called ______ forces.
Inter-molecular

14. The unit of surface tension in SI system is : ______.
Newton per metre (Nm-1)

15. Rain drops attain ______ shape to acquire minimum surface area.
Spherical

16. A tube with a very fine uniform bore throughout its length called a ______ tube.
Capillary

17. A towel soaks water on account of ______ action.
Capillary

18. Antiseptics have very ______ surface tension, so that can spread quickly.
Low

19. The relative viscosity of a liquid is the ratio of viscosity of a liquid to viscosity of ______.
Water

20. The terminal velocity of a sphere varies directly as the square of the ______ of it.

21. The viscosity of a liquid ______ with increase in temperature.
Decreases

22. Reynold’s number is the ratio of the inertial force per unit area to ______ force per unit area for a flowing iluid.
Viscous

23. The deep water runs ______ in a river.
Slow

24. The dimensional formula of stress is ______.
[ML-1 T-2]

25. The fractional change in the length, volume or shape of a body relative to that in its original configuration is a measure of the ______.
Strain

26. The deformation of an elastic body is directly proportional to the applied force within ______ limit.
Elastic

27. The normal force exerted by fluid on any surface in contact with its, called ______.
thrust

28. The liquid ______ its own level.
finds

29. A ______ is an instrument for measuring the pressure of the atmosphere.
barometer.

30. A siphon acts under ______ pressure.
Ans,
atmospheric

31. The upward thrust which any fluid exerts upon a body partly or completely immersed in it, is called its ______.
buoyancy

32. Relative density is a pure ______ having no unit.
number

33. Surface tension is a ______ quantity.
scalar

34. The critical velocity is fixed for a fluid for a given ______.
temperature

35. Bernoulli’s theorem is based on principle of conservation of ______.
energy

36. The elasticity of a material is ______ on hammering it.
increased

## WBBSE Class 9 Physical Science MCQ Questions Chapter 4.5 Separation of Mixtures

Well structured WBBSE Class 9 Physical Science MCQ Questions Chapter 4.5 Separation of Mixtures can serve as a valuable review tool before exams.

## Separation of Mixtures Class 9 WBBSE MCQ Questions

Multiple Choice Questions :

Question 1.
Which metal is lighter than water ?
(i) Calcium
(ii) Mercury
(iii) Sodium
(iv) Gold
Sodium

Question 2.
Which non-metal exists in liquid state at room temperature?
(i) Mercury
(ii) Bromine
(iii) Carbon
(iv) Sulphur
Bromine

Question 3.
Which natural element is hardest ?
(i) Fullerine
(ii) Iron
(iii) Gold
(iv) Diamond
Diamond

Question 4.
Name a substance whose properties are intermediate between metal and non-metal ?
(i) Germenium
(ii) Potassium
(iii) Iron
(iv) Carbon
Germenium

Question 5.
Which gas has the smell of rotten egg?
(i) Ammonia
(ii) Sulphuretted hydrogen
(iii) Carbon dioxide
(iv) Oxygen
Sulphuretted hydrogen.

Question 6.
What is the nature of aqueous solution of NaCl ?
(i) Acidic
(ii) Alkaline
(iii) Neutral
(iv) None of these.
Neutral.

Question 7.
Cite an example where both physical and chemical changes occur ?
(i) Incomplete burning of candle.
(ii) Burning of a magnesium ribbon
(iii) Slaking of lime
(iv) Melting of ice.
Incomplete burning of candle.

Question 8.
Name a non-metal that conducts heat and electricity ?
(i) Graphite
(ii) Sulphur
(iii) Diamond
(iv) Nitrogen
Graphite

Question 9.
MnO2 is a catalyst :
(i) positive
(ii) negative
(iii) both positive and negative
(iv) none of these

Question 10.
Heating of a platinum wire is a :
(i) physical change
(ii) chemical change
(iii) both physical and chemical change
(iv) none of these.
Physical change

Question 11.
The boiling point of water is :
(i) 100° C
(ii) -100° C
(iii) 0° C
(iv) 78° C
100° C

Question 12.
Which catalyst is used to prepare oxygen from KClO3 ?
(i) MnO
(ii) MnO2
(iii) Mn3 O4
(iv) V2 O5
MnO2

Question 13.
The method to separate sugar from its equeous solution a –
(i) evaporation
(ii) distillation
(iii) sedimentation
(iv) centrifugation
Evaporation

Question 14.
lodine and ethanol can be separated by –
(i) filtration
(ii) evaporation
(iii) distillation
(iv) fractional distillation
distillation

Question 15.
Mixture of carbon tetra-chloride and water are separated by using –
(i) funnel
(ii) separating funnel
(iii) breaker
(iv) fractionating column.
separating funnel

Question 16.
Boiling point of a liquid –
(i) decreases with increase of pressure
(ii) boiling point has no effect on pressure
(iii) increases with increase of pressure
(iv) do not always increase with increase of pressure.
Increases with increase of pressure.

Question 17.
The components of crude oil can be separated by –
(i) fractional distillation
(ii) distillation
(iii) fractional crystallisation
(iv) none of these
fractional distillation.

Fill in the blanks :

1. Quick lime when treated with water converts to _______ lime.
slaked

2. Graphite is _______ to touch.
slippery

3. NH4 Cl treated with NaOH liberates _______ gas.
ammonia

4. Rusting of iron is a _______ change.
chemical

5. Both physical and chemical changes occur in burning of _______.
candle

6. _______ is a liquid non-metal.
Bromine

7. Odour of _______ is pungent.
ammonia

8. _______ is a metalloid.
Arsenic/Antimony

9. Snow at the base of a glacier melts due to its heavy _______.
weight

10. _______ is a soft metal.
Sodium

11. Colour of copper suiphate crystal is _______.
blue

12. Aqueous solution of oxides of some solid _______ are acidic.
non-metals

13. Being non-metal _______ conducts electricity.
graphite

14. Water is added to conc. H2SO4. This is a _______ change.
physical

15. _______ are typically brittle.
Non-metals

16. _______ shows the characteristics of both metais and non-metals.
Metalloids

17. _______ is insoluble in water but soluble in carbon disulphide.
Sulphur.

18. Heating of platinum wire is an example of _______ change.
physical

19. Chemical change is _______.
permanent

20. Copper sulphate and sulphur are identified by _______.
solubility

21. Silver nitrate solution is added to sodium chloride solution to give a curdy white precipitate; the precipitate can be separated from the mixture by a process called _______.
filtration.

22. Glycerol is distilled under reduced pressure to avoid _______.
evaporation

23. The suspension of chalk in water can be separated by _______.
decomposition.

24. Kerosene is lighter and immiscible in water, they can be separated by using _______.
separating funnel.

## WBBSE Class 9 Physical Science MCQ Questions Chapter 4.4 Acids, Bases and Salts

Well structured WBBSE Class 9 Physical Science MCQ Questions Chapter 4.4 Acids, Bases and Salts can serve as a valuable review tool before exams.

## Acids, Bases and Salts Class 9 WBBSE MCQ Questions

Multiple Choice Questions :

Question 1.
Which element is present in all acids ?
(i) Hydrogen
(ii) Oxygen
(iii) Carbon
(iv) Nitrogen
Hydrogen

Question 2.
ZnO is –
(i) acidic
(ii) basic
(iii) amphoteric
(iv) neutral oxide
amphoteric

Question 3.
The weak acid is
(i) HCl
(ii) HNO3
(iii) H2 SO4
(iv) H2 CO3
H2 CO3

Question 4.
Aqueous solution of P2 O5 is
(i) HPO3
(ii) H3 PO4
(iii) H3 PO3
(iv) H3 PO2
H3 PO4

Question 5.
Methyl orange is a/an ___
(i) base
(ii) alkali
(iii) indicator
(iv) oxide
indicator

Question 6.
Minimum quantity of an indicator used in neutralisation reaction is ____
(i) 5 mL
(ii) 5.2 mL
(iii) 5.5 mL
(iv) 2-3 drops
2-3 drops

Question 7.
The aqueous solution of bases turn red litmus into ____
(i) blue
(ii) colourtess
(iii) violet
(iv) yellow
blue

Question 8.
NaCl is a/an ____
(i) normal
(ii) acid
(iii) basic
(iv) complex salt
normal

Question 9.
The strong acid is _____
(i) H2 SO4
(ii) H2 CO3
(iii) H3 PO4
(iv) CH3 COOH
H2 SO4

Question 10.
Caustic soda is a/an _______
(i) salt
(ii) weak base
(iii) strong base
(iv) acid
strong base

Question 11.
Sulphuric acid is a/an _________
(i) inorganic acid
(ii) organic acid
(iii) weak acid
(iv) hydracid
inorganic acid

Question 12.
Disodium hydrogen phosphate is a/an ______
(i) normal salt
(ii) basic salt
(iii) acid salt
(iv) double salt
Ans.
acid salt

Question 13.
Which of the following compounds is used to prepare vanishing colour
(i) NH4 OH
(ii) NaOH
(iii) Ca(OH)2
(iv) KOH
NH4 OH

Question 14.
Na2 SO4 is a/an ____
(i) normal salt
(ii) acid sait
(iii) basic salt
(iv) complex salt
normal salt

Question 15.
Indicator used for neutralisation reaction of H2 SO4 and NaOH is _____
(i) methyl orange
(ii) phenolphthalein
(iii) litmus
(iv) any indicator

Question 16.
The colour of phenolphthalein in dilute sulphuric acid solution becomes –
(i) red
(ii) yellow
(iii) blue
(iv) colourless
colourless

Question 17.
The colour of methyl orange in acidic solution becomes –
(i) red
(ii) yellow
(iii) blue
(iv) orange
red

Question 18.
Sulphuric acid contains
(i) 1
(ii) 2
(iii) 3
(iv) 4 replaceable hydrogen atom/atoms by a metal.
2

Question 19.
Ammonia is
(i) an acid
(ii) a base
(iii) a salt
(iv) none of these
a base

Question 20.
The acidity of CaO is ___
(i) 1
(ii) 2
(iii) 3
(iv) 4
2

Question 21.
The basicity of hydrochloric acid is
(i) 1
(ii) 2
(iii) 3
(iv) 4
1

Question 22.
Phosphoric acid is a –
(i) monobasic acid
(ii) dibasic acid
(iii) tribasic acid
(iv) none of these
tribasic acid

Question 23.
An aqueous solution turns blue litmus solution into red. Excess addition of which of the following solution to the above solution reverse the change –
(i) HCl solution
(ii) vinegar solution
(iii) H2 SO4 solution
(iv) caustic soda solution
caustic soda solution

Question 24.
Which of the following substance change the colour of pH paper to greenish – blue ?
(i) common salt
(ii) vinegar
(iii) an antacid
(iv) orange juice
An antacid

Question 25.
To protect tooth decay you are advised to brush your teeth regularly, the nature of commonly used paste is –
(i) neutral
(ii) acidic
(iii) basic
(iv) corrosive
Basic

Question 26.
If you soak a pH paper into gastric juices, it will indicate a pH value of –
(i) more than 7
(ii) less thati 7
(iii) equal to 7
(iv) less than 1
less than 7

Question 27.
Which of the following is responsible for acid rain ?
(i) N2
(ii) CH4
(iii) SO2 and NO2
(iv) H2
SO2 and NO2

Fill in the blanks :

1. An acidic oxide is called _______ of the acid, which forms with water.
anhydride

2. An oxide is a ______ of oxygen formed with another element.
compound

3. ______ oxides are some metallic oxides which behave both as an acidic and a basic oxide.
Amphoteric

4. CO, NO are examples of _____ oxide.
neutral

5. Basic oxides which are soluble in water produce _____ when they are disssolved in water.
alkalis

6. A base in general is an oxide or hydroxide of a ____ and when reacts with an acid produces _____ and water.
Metal, salt

7. _____ is a process in which acids and alkalis in equivalent quantities react in their aqueous solutions to produce salt and water.
Neutralisation

8. An acid salt is produced when insufficient quantity of a base reacts with a ______ acid.
polybasic

9. Normal salts are formed by the complete replacement of the replaceable ______ atoms from an acid molecule by a suitable substance.
hydrogen

10. Indicators are some weak organic acids or bases which indicate distinctive _____ in acid, alkali and neutral solutions.
colours

11. Substances with a pH value below 7 are _____
acidic

12. The aqueous solution of a base makes _____ litmus blue.
red

13. The colour of methyl orange in acid medium is _____ and that in alkaline medium is –
Pinkish-red, Yellow

14. An aqueous solution of an acid turns ______ litmus into red.
blue

15. pH scale is a scale that runs from ____ to _____.
0, 14

16. Na3 PO4 is a _____ salt.
normal

17. The substance used to determine the end point of neutralisation of an acid and a base is called _____.
indicator

18. Al2 O3 is an _____ oxide.
amphoteric

19. H2 O is a ______ oxide.
neutral

20. Pb(OH) NO3 is a ______ salt.
basic

21. HCN is hydracid but H2 SO3 is _____.
oxyacid

22. Concentrated _______ is a strong oxidising acid.
H2 SO4

23. An aqueous solution of acid must contain _____ ion.
H+

24. The formula of permanganic acid is _____.
HMnO4

25. P2 O5 is an _____ oxide.
acidic

26. Na2 HPO4 is an_____ salt.
acid

27. K4 [Fe(CN)6] is a _____ salt.
complex

28. Acetic acid is known as _____.
Vinegar

29. Acids have a ______ taste.
sour

30. Tooth enamel is made of ____.
Ca3 (PO4)2

31. pH value of pure water is ______.
0

32. Exact pH value of acid rain is _____.
5.6

33. ______ indicator is a such indicator which can determine the strength of solution.
universal

## WBBSE Class 9 Physical Science Solutions Chapter 4.3 Solution

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 4.3 Solution offer valuable context and analysis.

## WBBSE Class 9 Physical Science Chapter 4.3 Question Answer – Solution

Question 1.
Write down the name of an inorganic and an organic solvent.
Name of an inorganic solvent: water Name of an organic solvent: benzene

Question 2.
Write down the name of a substance whose solubility remains almost the same with rise of temperature.
Solubility remains almost the same with rise of temperature: Sodium chloride (NaCl).

Question 3.
Write down the name of a substance whose solubility decreases with the increase of temperature.
Solubility decreases with the increase of temperature: Calcium sulphate (CaSO4).

Question 4.
Write down the name of a substance whose solubility increases tremendously with the increase of temperature.
Solubility increases tremendously with the increase of temperature: e.g. Potassium nitrate (KNO3)

Question 5.
What is the unit of solubility ?
Solubility has no unit.

Question 6.
Which gas is soluble in soda water ?
Carbon dioxide (CO2) is soluble in soda water.

Question 7.
Give an example of a drying agent.
Drying agent : concentrated H2SO4.

Question 8.
Give a common example of colloidal solution.
Common example of colloidal solution : milk.

Question 9.
What are the components of a colloidal solution ?
Components of a colloidal solution :

• dispersed phase
• dispersion medium

Question 10.
Give one example of a salt having water of crystallisation.
Example of a salt having water of crystallisation :
Blue vitriol (CuSO4. 5H2O)

Question 11.
Mention one particulate matter in air that causes its pollution.
Particulate matter in air that causes its pollution : Fine particules of dust.

Question 12.
What are the sizes of the colloid particles?
Sizes of the colloid particles : 10-5 cm to 10-7 cm in diameter.

Question 13.
State whether solution is a mixture or compound.
Solution is a mixture.

Question 14.
Why edible salt (NaCl) becomes moist in the rainy season?
Edible salt (NaCl) becomes moist in rainy season due to the presence of deliquescent MgCL2 6H2O as impurity in it.

Question 15.
Name an efflorescent substance.
Efflorescent substance: Washing soda (Na2CO3.10H2O)

Question 16.
Name a deliquescent substance.
Deliquescent substance : Calcium chloride (CaCl2)

Question 17.
What happens if a saturated solution is cooled?
The cooled solution sheds the excess solute as crystals.

Question 18.
What is the effect of increase of pressure on the solublilty of a gas In water?
Increase of pressure increases solubility of a gas.

Question 19.
What is the effect of increase of pressure on the sotubility of a solid in water?
Increase of pressure does not cause any change of solubility of a solid in water.

Question 20.
What is occlusion?
Hydrogen get dissolved in spongy palladium in some similar metals. This phenomenon is called occlusion.

Question 21.
What is TEL?

Question 22.
What is epsome salt?
Epsome salt : MgSO4, 7H2O

Question 23.
What is SPM?
Suspended particulate matter (SPM)

Question 24.
What do you mean by smog ?
Smog is fog containing smoke.

Question 25.
How a saturated solution may be made unsaturated ?
A saturated solution may be made unsaturated either by :

• or, raising temperature of the solution.

Question 26.
State the biological importance of dissolved O2 in water.
Aquatic plants and animals can take oxygen for their respiration.

Question 27.
What is the effect of temperature on the solubility of KNO3 and CasO4 ?
Solubility of KNO3 increases with rise of temperature.
Solubility of CaSO4 decreases with rise of temperature.

Question 28.
How can you increases the solubility of a given volume of gas in water ?
An increase of pressure on the surface of water causes increase of solubility of gas in water.

Question 29.
Why does the CO2 gas rapidly bubbles out when the lid of its bottle is opened ?
CO2 gas rapidly bubbles out when the lid of its bottle is opened because on opening the lid the pressure on the solution suddenly decreases.

Question 30.
Which solution is more concentrated : 10g/L NaOh or 10 molar NaOH solution ?
10 molar NaOH solution.

Question 1.
What is a solution ?
Solution : A solution (or true solution) is a uniformly homogeneous mixture of two or more substances whose relative proportions may be varied upon a certain limit.

Question 2.
Name the different types of solution known to you in respect of concentration.
Classification of solution : Solutions are classified into three types based on concentration at a certain temperature. These are :

•  unsaturated
• saturated
• super saturated solutions.

Question 3.
What is an unsaturated solution ?
Unsaturated solution : At a particular temperature, an unsaturated solution is one in which the solvent is capable of dissolving further amount of the solute.

Question 4.
What is a saturated solution ?
Saturated solution : A saturated solution at a particular temperature is one in which the amount of the solvent has reached its maximum capacity of dissolving the solute.

Question 5.
What is a supersaturated solution ?
Supersaturated solution : A supersaturated solution is one, in which the amount of the solvent has dissolved more amount of the solute than is necessary to make a saturated solution at the particular temperature.

Question 6.
How can you detect a saturated sugar solution ?
Detection for saturated sugar solution : To the given solution, some amount of sugar is added into the solution and stirred. If the added sugar does not dissolve, the solution is said to be a saturated solution at that temperature.

Question 7.
How can you detect an unsaturated sugar solution ?
Detection for unsaturated sugar solution : To the tested solution some sugar is added and stirred. If the sugar readily dissolves, the given solution is said to be an unsaturated solution.

Question 8.
What do you mean by solute ?
Solute : The substances which are present in smaller quantities and gets dissolved are called solute.

Question 9.
What is meant by solvent ?
Solvent : The medium in which the solutes are uniformly dispersed through dissolution is called the solvent.

Question 10.
Define a colloid or colloidal solution.
Colloid or colloidal solution : A colloid or colloidal solution is a stable heterogeneous solution consisting of finely divided particles of a substance (of the size of 10-5 cm to 10-7 cm in diameter) uniformly dispersed in a continuous medium.

Question 11.
What do you mean by solubility ?
Solubility : Solubility of a given solute in a solvent is defined as the weight in grams of the solute dissolved in 100 grams of solvent so as to saturate the solution at a given temperature.

Question 12.
What is meant by ‘solubility is dependent on temperature’ ?
Solubility is dependent on temperature: It means, in general, solubility of a solid in a liquid solvent increases with increasing temperature and decreases with decreasing temperature. This rule is not obeyed in some cases.

Question 13.
What are the effects of temperature on solubility of CaSO4) KNO4, NaCl ?
Effect of temperature on solubility of CaSO4, KNO3, NaCl.
Solubility of CaSO4 decreases with increasing temperature.
Solubility of KNO3 increases rapidly with rise of temperature.
Solubility of NaCl remains almost unchanged with rise of temperature

Question 14.
What do you mean by ‘dispersed phase’ and ‘dispersion medium’ ?

• Dispersed phase : The component of colloid present in small amount and which behaves like a solute in a solution is called dispersed phase.
• Dispersion medium : The component of colloid present in excess amount and which behaves like a solvent in solution is called dispersion medium.

Question 15.
Define crystal.
Crystal : Crystals are homogeneous solid particles bounded by plane surfaces arranged symmetrically and meeting at sharp edges and forms a definite three-dimenstional geometrical shape.

Question 16.
What do you mean by crystallisation ?
Crystallisation : Crystallisation is a process by which crystals of a substance are obtained from its solution.

Question 17.
What is water of crystallisation ?
Water of crystallisation : The fixed number of water molecules that are associated with a crystal as an integral part of the constitution of the crystal is called water of crystallisation.
Example : Blue vitriol (CuSO4, 5H2O) has five molecules of water of crystallisation.

Question 18.
What is meant by efflorescent substance ?
Efflorescent substance : Efflorescent substances are those which crumble to powder when exposed to air due to partial or total loss of water molecules present in their crystalline structures.
Example : Washing soda (Na2CO3, 10H2O)

Question 19.
What do you mean by deliquescent substance ?
Deliquescent substance : Deliquescent substances are those solid which when exposed to atmosphere form concentrated solution dissolving in the moisture absorbed by them from air.
Example : Calcium chloride (CaCl2).

Question 20.
What happens if a saturated solution is cooled ?
If a hot saturated solution is cooled, the capacity of holding solute by the solution decreases. The cooled solution sheds the excess solute as crystals.

Question 21.
What are the effects of increase of pressure on the solubility of a gas and a solid solute in water ?
Increase of pressure increases solubility of a gas in water ; increase of pressure does not cause any change of solubility of a solid in water.

Question 22.
Why is temperature mentioned in defining solubility ?
In defining solubility of a substance, temperature is to be mentioned, because, with change of temperature solubility of most of the substances changes.

Question 23.
Why is a solution kept stirred continuously during its preparation ?
It is done to mix well the saturated and the unsaturated portions of the solution to bring about homogeneity of the solution.

Question 24.
What are hygroscopic substances ?
Hygroscopic substances : Certain substances exposed to air absorb moisture from air but are not dissolved in the absorbed water. These substances are called hygroscopic substances.

Question 25.
What are drying agents ?
Drying agents : Some substances have the property to absorb moisture from moisturous bodies present nearby. These substances are called drying agents.
Example : Concentrated H2SO4, Phosphorous pentoxide (P2O5), Silica gel.

Question 26.
What is Mother liquor ?
Mother liquor : In the process of crystalisation, the saturated solution left after separation of crystals is known as Mother liquor.

Question 27.
Define unit of concentration of solution in percentage.
Concentration of solution in percentage :
If V ml of the solution contains W g of the solute, percentage of the solution is $$\frac{W}{V}$$ × 100%

Question 28.
Define unit of concentration of solution in grams per litre.
Concentration of solution in grams per litre :
Its unit is g/L. When 1 litre (1000 ml) of the solution, contains w grams of the solute, its strength is w g/1L.

Question 1.
‘Solubility of A of t°C is y’ — what does it mean ?
‘Solubility of A at t°C is y’ — it means y’ g of A can produce a saturated solution when dissolved in a solvent at t°C.

Question 2.
How can you transform a saturated solution into an unsaturated one without adding more solvent ?
Without adding more solvent a saturated solution may be made unsaturated by raising its temperature at which the solubility of the solute increases appreciably and the solution thus turns unsaturated.

Question 3.
How does solubility of KNO3, NaCl and CaSO4 change with rise of temperature ?
Solubility of KNOt increases rapidly with rise of temperature.
Solubility of NaCl remains almost unchanged with rise of temperature.
Solubility of CaSO4 decreases with increasing temperature.

Question 4.
What is the cause of efflorescence ? Give one example of efflorescent substance.
Cause of efflorescence : Efflorescence happens only when the vapour pressure within the hydrated crystal at ordinary temperature is greater than the vapour pressure of the atmosphere. These hydrated crystals are called efflorescent substances.
Example : Na2CO3, 10H2O

Question 5.
What is the cause of deliquescence ? Give one example of deliquescent substance.
Cause of deliquescnces : Deliquenscence occurs when the vapour pressure of water in the deliquescent substance is less than the vapour pressure in the atmosphere at ordinary temperature.
Example : CaCl2

Question 6.
Why does effervescence occur when a soda water bottle is opened ?
Soda water is a solution of carbon dioxide in water, prepared under high pressure. For this reason when a bottle of soda water is opened, i.e. pressure on the liquid content in the bottle is reduced, effervescence or raising bubbles occur. These effervescences form, as a part of dissolved carbon dioxide gas, escapes through the liquid.

Question 7.
Why edible salt becomes moist in rainy season ?
Edible salt (NaCl) becomes moist in rainy season due to the presence of deliquescent substances like MgCl2 and CaCl2 as impurities in it.

Question 8.
How can you prepare a super saturated solution of a solid solute (hypo) at room temperature ?
Preparation of a super saturated solution : Super saturated solution can be prepared by heating a few crystals of sodium thiosulphate or hypo (Na2S2O3, 5H2O) in a test tube. The crystals appear to melt or they dissolve in their own water of crystallization and a very concentrated solution of the salt in water is obtained.

The test tube is plugged with cotton wool and allowed to cool to the room temperature. This solution is super saturated and even after cooling, no excess solute separates out. If a crystal of the salt is now added into this solution, the crystal groups in size and the whole liquid begins to solidify with evolution of heat.

Question 9.
Why does clear lime water turn milky when heated ?
Clear lime water turns milky when heated : Since solubility of slaked lime [Ca(OH)2] decreases with increase of temperature, clear lime water which is an aqueous solution of Ca(OH)2 or slaked lime turns milky when heated.
Reason : Due to decrease of solubility at a higher temperature, the excess undissolved slaked lime remains in suspension for which the solution appears milky.

Question 10.
Briefly describe the process of crystallisation.
Crystallisation : Crystallisation is a process from which crystal of a substance is obtained from its solution. Process of crystallisation for the preparation of crystal :

(a) From saturated solution of a substance : A hot saturated solution of the substance is slowly cooled and then the crystal of that substance is obtained.

(b) From unsaturated solution : An unsaturated solution is vapourised and thus a concentrated solution of it is obtained. Now if this solution is gradually cooled then crystals of the substance are obtained.

(c) Sublimation process : Iodine, camphor etc. are sublimed. If the sublimate so formed is cooled, then the crystals of the substances are deposited in the pot.

(d) From molten matter : Solid sulphur taken in a pot is heated to melt it and then by slowly cooling, the crystals of P-sulphurs are obtained.

Question 11.
What is colloid ? How does it differ from a true and a suspension state ?
Colloid : A colloid is a stable heterogenous solution consisting of finely divided particles of a substance (of the size of 10-5 cm to 10-7 cm in diameter) uniformly dispersed in a continuous medium. The component of colloid present in small amount and it behaves like a solute in a solution which is called dispersed phase. The component of colloid present in excess amount and which behaves like a solvent in a solution is called dispersion medium.

Identification of true solution, colloid and suspension : True solution, colloid and suspension are identified on the basis of particle size in it Size of a particle in colloidal state is 10-5 cm to 10-7 cm in diameter. The particle in true solution is 10-8 cm in diameter. The particle in suspension state is
10-8 cm in diameter.

Question 12.
How can an unsaturated solution be converted to saturated state without adding more solute ?
(i) Without adding more solute an unsaturated solution may be made saturated by evaporating off a part of the solvent when the remaining lesser quantity of solvent becomes saturated with the initial content of solute.

(ii) Also, by lowering the temperature of the given solution, it may be made saturated since the solute present in the solution may make it saturated at a lower temperature, because solubility of a substance in general decreases with lowering of temperature.

Question 13.
Describe briefly the mechanism of formation of a solution where a solid dissolves in a liquid.
Mechanism of formation of solution of a solid in the liquid : When a solid solute comes in contact with a liquid solvent, the tiny solid particles of diameter 10-8 cm or less leave the surface of the solid solute depending on temperature and as concentration of the solution increases, some solid particles return and get deposited on the surface of the lump of solute.

At the initial stage, the rate of leaving the solute surface increases and it slows down when concentration of the solution increases. If the rate of leaving the surface of solute is greater than that of their return, the solid dissolves totally.

Question 14.
Why does the colour of sky appear to be blue ?
Colour of sky appears to be blue due to the scattering of blue light by dust particles along with water suspended in air.

Question 15.
What is fire foam ?
Fire foam : Carbon dioxide froth made by mixing solution of sodium bicarbonate and alum is called fire foam. It is used in fire extinguishers. A protective colloid such as glue or dextrin is added to stabilise the foam.

Question 16.
Does formation of a solution accompany heat exchange ?
There is almost always heat changes accompanying formation of solutions. This means some solutes, when go into solution, heat is evolved and for some other solutes heat is absorbed.
e.g.

• NH4Cl, KNO3 etc. absorbs heat while they go into the solution i.e. the change is endothermic occurs, so their solubility increases with rise of temperature.
• Solubility of sodium chloride remains almost unchanged with rise of temperature.
• Heat evolves when calcium hydroxide, anhydrous sodium sulphate etc. go into solution. The change in such cases is exothermic, so solubility of them decreases with rise of temperature.

## WBBSE Class 9 Physical Science MCQ Questions Chapter 4.3 Solution

Well structured WBBSE Class 9 Physical Science MCQ Questions Chapter 4.3 Solution can serve as a valuable review tool before exams.

## Solution Class 9 WBBSE MCQ Questions

Multiple Choice Questions :

Question 1.
Solution is a :
(i) mixture
(ii) element
(iii) compound
(iv) none of these.
mixture.

Question 2.
The solvent of sulphur is :
(i) Water
(ii) Ethyl alcohol
(iii) Carbon disulphide
(iv) Benzene
Carbon disulphide

Question 3.
If a saturated solution is heated :
(i) the solution becomes unsaturated.
(ii) the solution becomes super saturated.
(iii) the solution remains saturated
The solution becomes unsaturated.

Question 4.
If more solvent is added to a saturated solution :
(i) the solution becomes super saturated
(ii) the solution becomes unsaturated
(iii) the solution remains saturated
The solution becomes unsaturated.

Question 5.
Solubility decreases with increasing temperature :
(i) KNO3
(ii) CaSO4
(iii) NaCl
(iv) none of these
CaSO4

Question 6.
When temperature rises, solubility of gas in liquid:
(i) decreases
(ii) increases
(iii) remains unaltered
(iv) None of these
decreases

Question 7.
If the size of the particles are 10-5 cm to 10-7 cm then the solution will be :
(i) true solution
(ii) suspension
(iii) colloid
(iv) none of these
colloid

Question 8.
Number of water molecules present in washing soda :
(i) 5
(ii) 6
(iii) 10
(iv) 7
10

Question 9.
Deliquescent substance is :
(i) Magnesium chloride
(ii) Washing soda
(iii) Glauber’s salt
(iv) Blue vitriol
Magnesium chloride

Question 10.
Fog is :
(i) a solution of liquid in gas
(ii) a solution of gas in gas
(iii) a solution of solid in gas
(iv) a solution of liquid in liquid.
a solution of liquid in gas.

Question 11.
Smoke is :
(i) a solution of gas in gas
(ii) a solution of carbon in gas
(iii) a solution of liquid in liquid
(iv) a solution of solid in solid.
a solution of Carbon in gas.

Question 12.
Solubility remains almost unchanged with rise of temperature :
(i) NaCl
(ii) CaSO4
(iii) Na2 SO4, 10 H2O
(iv) KNO3
NaCl

Question 13.
Phosphorus pentoxide is :
(i) efflorescent substance
(ii) deliquescent substance
(iii) drying agent
drying agent

Question 14.
Soluble in chloroform :
(i) sugar
(ii) common salt
(iii) oil
(iv) blue vitriol
oil

Question 15.
lodine is soluble in :
(I) water
(ii) aicohol
(iii) acetone
alcohol

Question 16.
Unit of concentration of solution is :
(i) g / L
(ii) g / m2
(iii) g / m
(iv) g / cm
g / L

Question 17.
Percentage strength is :
(i) 6 g
(ii) 6 kg
(iii) 6%
(iv) 6
6%

Question 18.
If excess amount of solute is dissolved in saturated solution then the solution is called :
(i) unsaturated solution
(ii) super saturated solution
(iii) colloid
(iv) emulsion
super saturated solution

Question 19.
The ratio of the components of a solution is
(i) fixed
(ii) may vary
(iii) may vary to any extent
(iv) may vary within a limit
may vary within a limit.

Question 20.
Aerated cold drinks contain CO2, sugar and water here ; solution is of
(i) Sugar
(ii) CO2
(iii) water
(iv) Sugar and CO2
Sugar and CO2

Question 21.
Which one is true solution ?
(i) solution of common salt
(ii) solution of chalk
(iii) milk
(iv) butter
Solution of common salt

Question 22.
Particle size of colloid is
(i) 10-8 cm
(ii) 10-4 cm
(iii) 10-3 cm
(iv) 10-5 – 10-7cm
10-5 – 10-7cm

Question 23.
Which will not diffuse ?
(i) Suspension
(ii) true solution
(iii) Coloids
(iv) none
Suspension

Question 24.
When liquid is dispersed in solid, the product is called :
(i) gel
(ii) sol
(iii) Emulsion
(iv) foam
gel

Question 25.
Which of the following in aqueous solution can enter into intermolecular space of water: (i) urea (ii) protein
(iii) DNA
(iv) starch
urea

Question 26.
Solubility of which increases with increase of temperature ? :
(i) O2
(ii) NH3
(iii) KNO3
(iv) SO2
KNO3

Question 27.
Which of the following solutions is unstable?
(i) Saturated
(ii) Unsaturated
(iii) Super saturated
(iv) Colloidal
Super saturated

Question 28.
Which of the following solvents is used to remove nail-polish :
(i) Ethyl alcohol
(ii) Methyl alcohol
(iii) Acctone
(iv) Terpentine oil
Acctone

Fill in the blanks :

1. Solute + solvent = _______.
Solution

2. A true solution is a ______ mixture.
homogeneous

3. The solubility of KNO3 in water ________ tremendously with the rise of temperature.
increases

4. A solution is _______ at a temperature if it can dissolve more solute or if its concentration increases.
unsaturated

5. A solution of low solute-content is a solution.
dilute

6. Solubility of CaSO4 _______ with increasing temperature.
decreases

7. A solution is saturated if it does not dissolve any more _______ at a given temperature and if its concentration remains unchanged.
solute

8. _____ is a typical state of matter which is intermediate between true solution state and coarse suspension state of matter.
Colloid

9. Efflorescent sustances crumble to powder when exposed to ________ due to partial or total loss of water molecules present in their crystalline structures.
air

10. Water of crystallisation are some waster molecules which are _______ attached to the molecule of a compound as essential building components of crystals.
chemically

11. Solubility of NaCl remains almost _______ with rise of temperature.
unchanged

12. Water is a _____ liquid solvent.
versatile

13. Soda water contains _______ under pressure.
carbon dioxide

14. The particle size (diameter) of colloid lies in between _____.
10-5 cm to 10-7 cm.

15. Calcium chloride is a ______ substance.
deliquescent

16. Glauber’s salt ( Na2 SO4,10 H2O) is an __________ substance.
efflorescent.

17. Crystals are homogeneous solid particles bounded by plane surfaces which meet at sharp edges and have a regular and definite _________ shapes.
geometric.

18. Solubility of gas in liquid ________ when temperature rises.
decreases

19. Emulsion is a colloid where small particle of one liquid are dispersed in another ________.
liquid

20. A solution is a ________ mixture of two or more substances in solid, liquid or gaseous state.
homogeneous.

21. Anhydrous copper sulphate is a ________ substance.
hygroscopic

22. Unit of concentration of solution is _______.
g/L

23. Sodium amalgam is a solution of sodium and _____.
mercury

24. A saturated solution can be converted to an unsaturated solution by _____ the solution (Heating/Cooling).
heating

25. Solubility of a gas in water increases by ______ pressure.
increasing

26. Solubility of a yas at constant pressure may be increased by _______ temperature.
decreasing

27. Sodium chloride remains in solution as _____.
ions.

28. Rate of crystallization from saturated solution may be increased by ______.
seeding

29. Solution is a ______ of a solute in a solvent.
homogenous mixture.

30. Colloidal solution contains two components, ____ and ______ .
dispersed phase/dispersed medium.

31. Milk is an example of ________ emulsion.
oil in water

32. In case of icecream ______ acts as a emulsifier.
gelatin

33. Ca(OH)2 shows a ______ of solubility with the _____ of temperature.
decrease, increase

34. _____ has no influence an the solubility of a solid ______ in a liqud solvent.
Pressure, solute

## WBBSE Class 9 Physical Science MCQ Questions Chapter 2 Force and Motion

Well structured WBBSE Class 9 Physical Science MCQ Questions Chapter 2 Force and Motion can serve as a valuable review tool before exams.

## Force and Motion Class 9 WBBSE MCQ Questions

Multiple Choice Questions :

Question 1.
Which of the following has no fixed melting point ?
(i) Ice
(ii) Wax
(iv) Iron
Wax.

Question 2.
The value of acceleration due to gravity :
(i) 980 m/sec
(ii) 9.81 m / sec2
(iii) 9810 m / sec
(iv) 98 m / sec2
9.81 m / sec2

Question 3.
If a body is taken in the moon then its weight will be :
(i) increased
(ii) decreased
(iii) same
(iv) zero
Decreased.

Question 4.
Soda lime is :
(i) Na2 CO3, 10 H2O
(ii) NaOH
(iii) Mixture of NaOH and CaO
(iv) NaCl
Mixture of NaOH and CaO.

Question 5.
Which is most fundamental ?
(i) mass
(ii) weight
(iii) density
mass.

Question 6.
What is the ultimate form of all energies ?
(i) Heat
(ii) Light
(iii) Sound
(iv) Chemical
Heat.

Question 7.
In an electric cell which type of energy changes to which other ?
(i) Chemical energy to electric energy
(ii) Heat energy to sound energy
(iii) Electric energy to chemical energy
(iv) Chemical energy to sound energy.
Chemical energy to electric energy.

Question 8.
When a body is taken to a high altitude from the earth, what changes of mass and weight of the body are observed ?
(i) Mass remains same, weight decreases
(ii) Weight remains same, mass increases
(iii) Both mass and weight increase
(iv) Both mass and weight decrease
Mass remains same, weight decreases.

Question 9.
What is the Einstein’s mass energy-equation ?
(i) E = mc2
(ii) E = m2c2
(iii) E = m2c
(iv) E2 = mc2
E = m c2.

Question 10.
A non-conventional fuel is :
(i) natural gas
(ii) organic gas
(iii) petroleum gas
(iv) coal
Organic gas.

Question 11.
Law of conservation of mass was emunicated by :
(i) Lavoisier
(ii) Dalton
(iii) Proust
(iv) Landolt.
Lavoisier.

Question 12.
During photosynthesis, light energy is converted into :
(i) chemical energy
(ii) sound energy
(iii) electric energy
(iv) heat energy
Chemical energy.

Question 13.
The force by which a body is attracted towards the centre of the earth is called :
(i) mass
(ii) weight
(iii) density of the body
Weight.

Question 14.
Absolute unit of weight in CGS system is :
(i) newton
(ii) dyne
(iii) Joule
Dyne.

Question 15.
The ability of doing work is known as :
(i) mass
(ii) weight
(iii) energy
Energy.

Question 16.
During nuciear fission, atomic energy is converted into :
(i) heat energy
(ii) electric energy
(iii) magnetic energy
Heat energy.

Question 17.
(i) 1.8 × 109 megawatt
(ii) 18 × 109 megawatt
(iii) 20 × 109 megawatt
(iv) 2.1 × 109 megawatt
18 × 109 megawatt.

Question 18.
In photo-electric cells, light energy is converted into :
(i) sound energy
(ii) magnetic energy
(iii) electrical energy
Electrical energy.

Question 19.
The value of acceleration due to gravity at the centre of the earth is :
(i) 0
(ii) less than 0 (zero)
(iii) greater than 0 (zero)
0 (zero).

Question 20.
If a body covers equal distances in equal time intervals, then it is :
(i) at rest
(ii) moving with uniform speed
(iii) moving with uniform velocity
(iv) moving with uniform acceleration
Moving with uniform speed.

Question 21.
If a body moves with a constant speed, the distance – time graph is
(i) a straight line
(ii) a circle
(iii) a line like a staircase
(iv) a polygon
A straight line

Question 22.
The area under the speed-time graph is a :
(i) circle
(ii) parabola
(iii) distance
(iv) none of these
distance

Question 23.
The slope of a distance-time graph is :
(i) velocity
(ii) acceleration
(iii) displacement
(iv) speed
Speed

Question 24.
The momentum of a body of given mass is proportional to its
(i) volume
(ii) shape
(iii) speed
(iv) density
speed

Question 25.
Which of the following has the largest inertia ?
(i) a pin
(iii) an orange
(iv) a brick

Question 26.
A body acted upon by a force must have :
(i) velocity
(ii) displacement
(iii) acceleration
(iv) none of these
acceleration

Fill in the blanks :

1. Mass and energy cannot be always considered as ______ quantities.
absolute.

2. Einstein showed that in high energy atomic reactions, a small part of ______ of the reactants transforms to energy.
mass.

3. After a few changes and transformations, almost all kinds of energy may be proved to originate from the ______.
sun.

4. Indian philosophers enunciated that anything that ______ is unperishable.
exists.

5. An energy can produce mechanical work directly or after undergoing some ______ transformations.
intermediate.

6. Every form of energy ultimately transforms to ______ energy directly or after some intermediate transformations.
heat.

7. Energy can neither be created nor destroyed, only one form of ______ energy to other forms.
transforms.

8. Electric energy transforms to ______ energy in electric lamps.
light.

9. Mass of a body is the quantity of ______ it is made of.
matter.

10. Mass is more fundamental than ______
weight.

11. Mass of a body is measured by a common balance and ______ of a body is measured with the help of a spring balance.
weight.

12. Weight is the ______ that a material body experiences towards the centre of the earth due to the gravitational pull of the earth.
force.

13. The weight of a body is ______ in different places of the world.
different.

14. Coal, petroleum, natural gas are – sources of energy.
non-renewable.

15. If the earth’s gravitational attraction ceases, the acceleration due to gravity also ______
ceases.

16. Mass of a body × ______ = Weight of body.
Acceleration due to gravity.

17. Energy is defined as ______ to perform work.
capacity.

18. Weight of a body is a ______ quantity.
vector.

19. Mass is an ______ property of a body.
intrinsic.

20. The energy of a moving body possessed by virtue of its ______ is called the kinetic energy.
motion.

21. Mass of a body is the ______ of matter it is made of.
quantity.

22. To accelerate a body, a must apply ______ on it.
force.

23. The SI unit of force is ______.
newton

24. A body at rest will remain at ______ it no unbalanced force is applied.
rest

25. Action and reaction forces act on ______ bodies.
different

26. The force is equal to the product of mass and ______ of the body.
acceleration.

## WBBSE Class 9 Physical Science Solutions Chapter 4.5 Separation of Mixtures

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 4.5 Separation of Mixtures offer valuable context and analysis.

## WBBSE Class 9 Physical Science Chapter 4.5 Question Answer – Separation of Mixtures

Question 1.
Name a metal and a non-metal which exists in liquid state at room temperature.
Mercury is a liquid metal at room temperature.
Bromine is a liquid non-metal at room temperature.

Question 2.
Name a non-mental heavier than water.
Iodine is a non-metal heavier than water

Question 3.
What type of change occurs when milk is converted to curd ?
Chemical change occurs when milk is converted to curd.

Question 4.
What type of change occurs when quick lime is treated with water ?
Chemical change occurs when quick lime is treated with water.

Question 5.
Name a non-metal having lustre.
Iodine is a non-metal having lustre.

Question 6.
Name a metal lighter than water.
Lithium is a metal lighter than water.

Question 7.
Mention chemical reaction which is influenced by pressure.
In crackers, a mixture of potassium chlorate and sulphur explodes under pressure.

Question 8.
Mention chemical reaction which is influenced by contact.
Quick lime in contact with water produces slaked lime with evolution of heat.

Question 9.
Which gas has the smell of rotten egg ?
Hydrogen sulphide (H2S) gas has the smell of rotten egg.

Question 10.
Mention a chemical reaction that is influenced by a catalyst.
When a mixture of MnO2 and KClO3 are heated, oxygen gas is evolved. In this reaction MnO2 acts as a catalyst.

Question 11.
Name two solids which may be identified by colour.
The colour of blue vitriol or hydrated copper sulphate is blue. The colour of chalk powder is white.

Question 12.
Mention a chemical reaction where heat is absorbed.
Quick lime in contact with water produces slaked lime with evolution of heat.

Question 13.
Name a non-mental that conducts electricity.
Graphite or Gas carbon, a non-metal conducts electricity.

Question 14.
Name two metalloids.
Arsenic (As) and Antimony (Sb) are two metalloids.

Question 15.
(i) concentrated sulphuric acid and
(ii) water. State whether a physical change occurs or a chemical change during these two incidents.
(i) Chemical change occurs when sugar is added to concentrated sulphuric acid.
(ii) Physical change occurs when sugar is added to water.

Question 16.
Name an electropositive metal and an electropositive non-metal.
Sodium is an electropositive metal.
Hydrogen is an electropositive non-metal.

Question 17.
Cite one physical change where heat is absorbed.
When ammonium chloride or ammonium nitrate is dissolved in water heat is absorbed.

Question 18.
Name a soft metal.
Sodium (Na) is a soft metal.

Question 19.
Give an example where physical and chemical changes take place simultaneously.
Burning of candle is an example of simultaneous occurrence of both physical and chemical change.

Question 20.
Give an example of a slow reaction.
Rusting of iron is an example of a slow reaction.

Question 21.
State one chemical change where heat is absorbed.
Heat is absorbed when nitrogen and oxygen combine to form nitric oxide.

Question 22.
Give an example of a metal which reacts both with acid and alkali.
Zinc is the metal which reacts both with acid and alkali.

Question 23.
Which type of ion is formed by hydrogen in NaH ?
H(-) ion is formed by hydrogen in NaH.

Question 24.
Give an example of natural physical change.
Melting of glacier is an example of natural physical change.

Question 25.
Give an example of a natural chemical change.
Forest fire is an example of natural chemical change.

Question 1.
Define properties of matter ?
Properties of matter : Each and every substance has its special characteristics by which we can identify it. These characteristics of matter are known as the properties of matter.

Question 2.
What do you mean by physical properties of matter ?
Physical properties of matter : Physical properties of matter are those which are observed externally and can be determined without changing the composition of matter.

Question 3.
What are the different forms of matter ?
Matters can exist normally in three forms.
These forms are :

• solid
• liquid
• gas or vapour

Question 4.
Define melting point of a solid.
Melting point of a solid: Melting point of a solid is the temperature at which the solid begins to transform to liquid under normal pressure, the temperature remains constant till the whole mass of the solid converts to liquid.

Question 5.
Define boiling point of a liquid.
Boiling point of a liquid: Boiling point of a liquid is the temperature at which the liquid begins to transform rapidly to its vapour state under normal atmospheric pressure and the temperature remains constant until whole mass of the liquid converts to its vapour.

Question 6.
What do you mean by chemical properties of matter ?
Chemical properties of matter: Chemical properties of matter are those which are manifested when the matter undergoes chemical changes involving the change of its composition.

Question 7.
What do you mean by physical change ?
Physical change : The physical change is a temporary change in which internal structure of the molecules of the component remains unchanged, only physical state of matter is changed.

Question 8.
What do you mean by chemical change ?
Chemical change : A chemical change is a permanent change in which the substance gives rise to one or more new substances with different compositions and properties.

Question 9.
Which of the following are physical changes and which are chemical changes ? Give one reason for each answer.
(i) Lime is treated with water
(ii) Water is boiled to steam
(iii) Rice is converted to puffed rice
(iv) Sugar is dissolved in water
(v) Iron is magnetised
(vi) Souring of milk
(vii) Coal is burnt in air
(viii) A platinum wire is heated
(ix) Rusting of iron
(x) Burning of magnesium wire
(xi) Melting of ice
(xi) Burning of candle.
(i) Lime is treated with water: This is a chemical change.
When quick lime is added to water, it boils and ultimately slaked lime is formed. It is heavier than quick lime having different properties also. So it is a chemical change.
CaO + H2O → Ca (OH)2 + heat

(ii) Water is boiled to steam: This is a physical change.
After some time steam returns to water, so it is a temporary change.

(iii) Rice is converted to puffed rice: This is a chemical change. Puffed rice cannot be converted to rice again, so it is a permanent change.

(iv) Sugar is dissolved in water: This is a physical change. A lump of sugar breaks into tiny pieces while it dissolves in water. If the solution is now heated to boil off water, sugar is again obtained. So it is a temporary change.

(v) Iron is magnetised: This is a physical change. An iron bar acquires magnetism when it is rubbed with a magnet several times. There has been only a rearrangement of its molecules. The new property acquired by the iron is temporary because when it is heated strongly, its magnetic property is removed.

(vi) Souring of milk: Souring of milk is a chemical change. In this process, milk is converted to curd which is sour in taste. The sour taste is due to the conversion of fat molecules of milk to sour lactic acid. Curd thus produced cannot be converted back to milk.

(vii) Coal is burnt in air: Burning of coal in air is a chemical change. When coal is burnt in air, carbon dioxide gas and some ashes produce from which the original substance cannot be recovered. So it is a permanent change.

(viii) A platinum wive is heated: This is a physical change. When platinum wire is heated it burns becoming white hot and radiates light but there is no change in the composition of the matter. It regains its initial state on cooling.

(ix) Rusting of iron: This is a chemical change. Rusting is nothing but hydrated ferric oxide which is formed by the reaction of iron, oxygen and water. It is heavier than iron. Iron and rusting of iron are different in composition. So, it is a permanent change.

(x) Burning of magnesium wire : This is a chemical change.
When magnesium burns in air or oxygen, magnesium oxide is produced.
2Mg + O2 = 2MgO.

When magnesium is burnt in air, Mg3 N2 also produces. Magnesium cannot be recovered from these new substances. So, this is a permanent change.

(xi) Melting of ice: This is a physical change. No new substance produces during this change. Water can be cooled back to ice. So, this is a temporary change.

(xii) Burning of Candle: This is a chemical change. New substances like carbon dioxide and water vapour are produced during this change. Original substance cannot be obtained from these new substances. So, this is a permanent change.

Question 10.
Explain one natural physical change.
Natural physical change (Melting of Glacier): Ice exists in the peak of a mountain but in summer it flows down as water in the plane surface or earth. Glacier, a slowly moving mass of ice is transformed into water when pressure, temperature and other geographical conditions change.

Water thus produced is ultimately mixed with sea. In summer, water from river, sea and other sources are again transformed to vapour and is condensed to ice in peak of mountain in cold. So melting of glacier is a temporary change. So, melting of glacier is an example of natural physical change.

Question 11.
Explain one natural chemical change.
Natural chemical change (Forest fire) : Far from seaside, in summer or any hot condition fire is formed in the forest due to friction of woods. The fire spreads quickly in the forest. As a result the trees and the bushes burn forming carbon dioxide and the wood charcoal with some other organic materials. So, forest fire is a permanent change.For this reason, forest fire is considered as natural chemical change.

Question 12.
Physical and chemical changes take place simultaneously when a candle burns — Explain.
Simultaneous occurrence of physical and chemical change: When a candle burns in air, a portion of it melts. The molten part when cooled returns to solid wax, the material of candle. So this part is a physical change.

Major part of the candle converts into water vapour and carbon dioxide gas. Original portion of the candle cannot be obtained from these water vapour and carbon dioxide. So this is a chemical change.
So, in this case, physical and chemical changes occur at the same time.

Question 13.
Give an example where physical and chemical changes take place simultaneously.
When water is sprayed over quick lime, and much heat generates and quick lime converts to slaked lime. The produced heat converts a part of water to steam which is a physical change since steam may be cooled to water again.

The conversion of quick lime to slaked lime is a chemical change as the slaked lime thus formed cannot be converted to its original form (quick lime) easily. So, both the physical and chemical changes occur simultaneously.

Question 14.
Give the example of a slow reaction.
Slow reaction: The reaction in which the amount of activation energy is high, is called slow reaction.
Example : Organic compounds or some of the covalent compounds undergo chemical reactions slowly.

Question 15.
Give the example of a fast reaction.
Fast reaction : The reaction in which the amount of activation energy is low, called fast reaction at given temperature. The time required for the completion of such reactions is about 10-14 to 10-15 second.

Example : Ionic compounds which are inorganic in nature normally undergo fast reaction.

• NaCl + AgNO3 → AgCl ↓ + NaNO3
• BaCl2 + H2SO4 → BaSO4 ↓ + 2HCl

Question 16.
What do you mean by catalyst and catalysis?
Catalyst and catalysis : A catalyst is a substance that alters the rate of a chemical reaction without itself being used up and can be recovered unchanged chemically at the end of a chemical reaction. The phenomenon of acceleration or retardation of chemical reactions by the presence of a catalyst is called catalysis.

Question 17.
Explain positive catalyst with example.
Positive catalyst: Catalyst which can accelerate the rate of chemical reaction is called positive catalyst.
Example:

Question 18.
Explain negative catalyst with example.
Negative catalyst: Catalyst which can retard the rate of the themical reaction is called negative catalyst.

(ii) Antifreezes like glycerol which retard the rusting of the machines.

Question 19.
What do you mean by exothermic change?
Exothermic change: Exothermic change is one in which a substance undergoing a physical change or a chemical change releases heat into its surroundings.

Examples :
(j) Exothermic physical changes: When caustic soda (NaOH) dissolves in water or when concentrated sulphuric acid (H2SO4) is mixed in water, plenty of heat evolves in each of the physical change 8.
(ii) Exothermic chemical changes:

• C + O2 = CO2 + heat (94,000 cal)
• CaO + H2O = Ca(OH)2 + heat

Question 20.
What do you mean by endothermic change?
Endothermic change: Endothermic change is one where a substance undergoing physical or chemical change takes heat from its surroundings.

Examples :
(i) Endothermic physical changes : In the dissolution process of ammonium chloride (NH4Cl) or ammonium nitrate (NH4NO3) in water, heat is absorbed.
(ii) Endothermic chemical changes:

• C + 2S = CS2 — heat (25,000 cal)
• N2 + O2 = 2NO — heat (43,000 cal)

Question 21.
What is fractional distillation?
Fractional distillation : The process by which two or more miscible liquids are separated by distillation using the difference in their boiling point is known as fractional distillation. When the boiling points of two or more miscible liquids differ by about 15°C — 20°C, these are separated by simple fractional distillation.

Question 22.
How two immiscible liquids are separated?
Separation of two immiscible liquids: When two different liquids do not mutually dissolve in each other but remain floating one above the other, it is called a mixture of two immiscible liquids. They are separated with the help of a separating funnel.

Question 23.
What is chromatography?
Chromatography : It is a modern technique by which mixture of different substances are separated. In this method due to difference in adsorption of different substances in solid phase (adsorbent) and the difference in migration of the substances in the mobile phase (liquid or gas) various substances are separated.

Question 24.
What do you mean by paper chromatograpny?
Paper chromutographv : This is a very easy technique to separate the various organic dyes present in the writing ink or printing ink.

Question 25.
What are the advantages of chromatography?

• A small amount of the compound present in the mixture can be separated.
• The properties of the individuals present in the mixture do not alter.
• This is very easier method to separate the different components present in the mixture.

Question 26.
What do you mean by sublimation?
Sublimation: There are some solids which on heating directly transform into vapour phase without transforming through the intermediate liquid state. This phenomenon is known as sublimation. Using this method two different solids ammonium chloride (NH4Cl) and sand (SiO9) can be separated.

Question 27.
What are metals?
The elements having lustre, normally solid and heavy, which conduct heat and electricity, electro-positive in nature producing metallic sound on striking are called metals.
Example : Fe, Al, Zn, Na, Ag etc.

Question 28.
What do you mean by non-metals
Non -Metals: The elements which do not possess any lustre, normally exist in liquid and gaseous state, poor conducting ability of heat and electricity, electronegative in character are called non metals.
Example : H2, O2, Cl2, N2, C, S, P etc.

Question 29.
What is a metalioid ?
Metalloids : The elements which have both metallic and non metallic characters are known as metafloids. Arsenic (As), antimony (Sb).

Question 30.
What are reasons for separting the components of mixture?
The components of a mixture are separated because of the following reasons :

• To get a pure sample of a substance.
• To remove any undesirable or harmful components.
• To obtain the useful components of a mixture.

Question 31.
What is distillation?
Distillation: The process of converting a liquid into its vapour by heating and the subsequent condensation of the vapour back into the original liquid is known as distillation.

Question 32.
What is separatory funnel?
It is an apparatus used for sepating immiscible liquids. The liquids do not mix with each others and due to the difference in densities, the liquids remain in separate layers in the sepratory funnel.

Question 1.
Give an example for each of the chemicaì changes influenced by
(a) Contact
(b) Heat
(c) Pressure
(d) Light
(a) Contact: Quick lime (CaO) in contact with water produces slaked lime [Ca(OH)2] with generation of heat.
(b) Heat: When mercury is heated in air, red mercuric oxide is formed.”
2Hg + O2 = 2HgO (red)
(c) In Haber’s process nitrogen combines with hydrogen at 200 atmospheric pressure forming ammonia.

(d) Light induces and regulates the chemical reactions involved in photography.

Question 2.
Explain with examples how matter is identified with the help of physical properties.
Matters are identified by physical properties :
(a) Physical State: At ordinary conditions all matters do not exist in the same state.
e.g. at ordinary temperature, gold, silver, iron all are solid.

Water, milk, oil are liquid.
Hydrogen, oxygen, carbon dioxide etc. are gaseous.

(ii) Touch: Many substances may be identified by touching.
e.g. Slippery nature of graphite is easily distinguished with the coarse nature of chalk.

(iii) Smell : Different substances have different smell.
e.g. Ammonia gas has pungent smell, hydrogen suiphide has the distinctive smell of rotten egg and oxygen gas is odourless.

(iv) Colour : Some substances have distinctive colours which help us to identity them.
e.g. Blue vitriol (hydrated copper sulphate) has blue colour while gold has a bright yellow colour.

(v) Solubility : Different substances have different solubilities in different solvents.
e.g. Sugar is soluble in water but not in petrol. On the other hand sulphur is not soluble in water but soluble in carbon disuiphide.

(vi) Magnetic property : Different substances may be distinguished with their different magnetic properties.
e.g. Iron, cobalt, nickel and some of their alloys may be magnetised or attracted by a magnet while gold, copper etc. have no such property.

(vii) Melting point and boiling point: Different crystalline solids have different melting points and they are identified by their melting points or freezing point. Again different pure liquids have different boiling point and they are identified by their boiling point.
e.g. At 1 atm. pure ice has melting point 0°C while pure water has boiling point 100°C.

Question 3.
Explain with examples how matter is identified with the help of chemical properties.
Matters are identified by chemical properties:
(i) Action of heat:

But sugar when treated with water, it simply dissolves without producing any chemical change.

(iii) Action with acid:
Zn (Zinc) + (dilute) H2SO4 → ZnSO4 + H2
But the same acid in ordinary condition has no action on copper.

(iv) Action with alkalis:
NH4Cl + NaOH → NaCl + NH3 ↑ + H2O
But sodium chloride does not react with alkali.

Question 4.
Compare between physical change and chemical change.
Difference between physical and chemical change:

Question 5.
What are the characteristics of catalyst?
Characteristics of catalyst :

• The catalyst is unchanged chemically at the end of the reaction.
• Only a small quantity of the catalyst is generally needed.
• The catalyst does not alter the position of equilibrium in a reversible reaction.
• The catalyst does not initiate the reaction.
• The catalyst is generally specific in its action.
• The catalyst cannot alter the nature of the products of the reaction.
• A catalyst has an optimum temperature at which the efficiency of the catalyst is maximum.
• A catalyst is poisoned by certain substances.
• The activity of a catalyst is enhanced by the presence of substances called promoters.

Question 6.
Describe how two miscible liquids may be seperated by fractional distillation.
Separation of two miscible liquids by fractional distillation:
When the boiling points of two or more miscible liquids differ by about 15°C — 20°C, these are separated by simple fractional distillation.

Procedure: The liquid mixture is kept in a distilation flask fitted with a Leibig’s condenser. The other end of the condenser is connected with a receiving flask for collection of the distillate. Now the liquid mixture is heated. The volatile liquid i.e. liquid having lower boiling point through the condenser in the form of vapour.

The vapour is condensed to liquid and collected in a receiver. Liquid having higher boiling point is left in the distillation flask. By controlling rate of heating and temperature of the fractionating column, a good separation of the components is possible.

Question 7.
Discuss the method of separation of two immiscible liquids by separating funnel.
Separation of two immiscible liquids by separating funnel:
A mixture of two immiscible liquids are easily separated by using separating funnel. Each liquid forms its own liquid layer due to difference in density.

Procedure: Two immiscible liquids are kept in a separating funnel and are shaken for few minutes keeping the stop-cock closed. The liquid mixture is allowed to stand for half an hour. The immiscible liquids separate into two distinct layer.

The liquid with lower density remains in the upper layer and the liquid with higher density will be deposited in the lower layer. The denser liquid in the lower layer can be easily run out by opening the stop-cock lying in the bottom of the funnel and collected in a conical flask. Later, the liquid in the upper layer may be collected in another flask.

Question 8.
Briefly describe how the colouring matters of ink can be separated by paper chromatoqraphy.
Separation of colouring matters of ink by paper chromatography:
Paper chromatography: It is a very easy technique to separate the colouring matters present in the ink.

Materials required :

• Solvent : Water, ethanol, acetone etc.
• Chroniatographic chamber : A glass jar fitted with a tightly fitting lid.

Procedure :

• A spot of ink is applied on and near the lower edge of a long strip of filter paper. The spot is allowed to dry.
• The paper is hung in an airtight container that does not absorb solvent vapour.
• A glass jar fitted with a tightly fitting lid may serve the purpose as a chromatographic chamber.
• Enough quantity of a solvent (water, ethanol, acetone etc.) is introduced in the flask, so that the level of solvent almost, but not quite, reaches the spot.
• The solvent rises in the porous paper by capillary action. The components of the ink also travel along with it. The various components in the ink lie at different heights in the paper for their differences of speeds in the solvent on the paper.
• The different components of different colours are visible at different levels on the filter paper.
• The colourless substance may be detected by spraying with a substance that reacts to give a coloured spot.
• Different coloured portions of the paper are cut off which are then treated separately in suitable solvents and the components of ink are recovered.

Question 9.
How will you separate ammonium chloride and sand by the method of sublimation?
Separation of ammonium chloride and sand by the method of sublimation:
Procedure :

• A small quantity of a mixture of ammonium chloride and sand is taken in a flat basin.
• A funnel is inverted over it. The outer surface of the funnel is wrapped with a water-soaked filter paper. The end portion of the funnel is plugged with a piece of cotton wool to prevent the vapours from escaping.
• The basin is then gently heated on a sand bath. The vaporised ammonium chloride is coming in contact with the colder wall of the funnel condenser kept there as powdered ammonium chloride.
• The sand remains in the flat basin, ammonium chloride is scrapped off. In this way ammonium chloride and sand are separated.

Question 10.
State three basic characteristics of metal and non-metal with respect to
(a) ion formation
b) reaction with oxygen
(c) conduction of electricity and heat.
(a) Ion formation : Metals form positive ions by loss of electron.
e.g. Na – e → Na+ ; Mg – 2e → Mg2+ ; Al – 3e → Al3+

Non-metals form negative ions by gaining electron.
e.g. Cl + e → Cl ; O + 2e → O2- ; N + 3e → N3-

(b) Reaction with oxygen : Almost all metals (except Ag, Au) react with oxygen to produce metallic oxides; aqueous solution of some of these like Na2O, K2O are alkali.
Na + O2 → Na2O; Na2O + H2O = 2 NaOH
K + O2 → K2O ; K2O + H2O = 2 KOH

Oxides of non-metals are usually acidic in nature. Aqueous solution of oxides of C, S, P etc. are acidic.
C + O2 → CO2 ; CO2 + H2O = H2CO3 (Carbonic acid)
S + O2 → SO2 ; SO2 + H2O = H2SO3 (Sulphurous acid)

(c) Conduction of electricity : Metals are good conductors of heat and electricity.
Non-metals are usually bad conductors of heat and electricity.
Exception: Graphite, though a non-metal is a good conductor of heat and electricity.

## WBBSE Class 9 Physical Science MCQ Questions Chapter 1 Measurement

Well structured WBBSE Class 9 Physical Science MCQ Questions Chapter 1 Measurement can serve as a valuable review tool before exams.

## Measurement Class 9 WBBSE MCQ Questions

Multiple Choice Questions :

Question 1.
What is the SI unit of temperature ?
(i) calorie
(ii) kelvin
Kelvin.

Question 2.
Which unit should be chosen to measure the distance between two stars ?
(i) kilometre
(ii) femtometre
(iii) light year
light year.

Question 3.
Which physical quantity has the dimension [MLT-2] ?
(i) velocity
(ii) acceleration
(iii) temperature
acceleration.

Question 4.
What is the unit of atomic weight ?
(i) gram
(ii) milligram
(iii) no unit
no unit.

Question 5.
At what temperature density of water is maximum ?
(i) 0°C
(ii) 4°C
(iii) 1 K
4°C.

Question 6.
Of the following quantities, which is scaiar quantity ?
(i) velocity
(ii) time
(iii) weight
(iv) force
time.

Question 7.
The dimension of velocity is :
(i) [LT-1]
(ii) [M L T-2]
(iii) [M L-1 L-2]
(iv) [M L T-1]
[LT-1].

Question 8.
Which one is not fundamental unit ?
(i) metre
(ii) litre
(iii) kilogram
(iv) second
litre.

Question 9.
Light year is the unit of :
(i) time
(ii) distance
(iii) temperature
distance.

Question 10.
To measure the diameter of an atom, the unit is used :
(i) ohm
(ii) metre
(iii) fermi
(iv) millilitre
fermi.

Question 11.
1 fermi is :
(i) 10-15 metre
(ii) 10-10 metre
(iii) 10-5 metre.
10-15 metre.

Question 12.
1 X-unit is :
(i) 10-13 cm
(ii) 10-12 cm
(iii) 10-11 cm
10-11 cm.

Question 13.
1 light year is :
(i) 9.45 × 1010 km
(ii) 9.47 × 1011 km
(iii) 9.467 × 1012 km.
9.467 × 1012 km.

Question 14.
Which one is scalar quantity :
(i) acceleration
(ii) velocity
(iii) work
work.

Question 15.
An object has density 4 g c .c. and volume 20 c.c.. What will be the mass of the object ?
(i) 80 g
(ii) 40 g
(iii) 5 g.
80 g.

Question 16.
Identify the vector quantity :
(i) mass
(ii) volume
(iii) time
(iv) weight
Weight.

Question 17.
The unit of volume is :
(i) fundamental unit
(ii) derived unit
(iii) none of these
derived unit.

Question 18.
The density of Hg is :
(i) 13.6 g c. c.
(ii) 12.6 g c. c.
(iii) 11.6 g c. c.
13.6 g c. c.

Question 19.
The watch used in run competition is :
(i) pendulum clock
(ii) stopwatch
(iii) table clock
stopwatch.

Question 20.
The dimension of Retardation is :
(i) [LT-1]
(ii) [LT-2]
(iii) [LT]
[LT-2]

Question 21.
1 per sec is :
(i) 30.84 km
(ii) 29.75 km
(iii) 28.82 km
30.84 km

Question 22.
1 Astronomical unit (Au) is :
(i) 1.495 × 108 km
(ii) 2.57 km
(iii) 3.82 km
1.495 × 108 km .

Question 23.
The dimensions of force are :
(i) [M2 L T-2]
(ii) [M L-2 T-2]
(iii) [M L T2]
(iv) [MLT-2]
[MLT-2]

Question 24.
The prefix mega stands for
(i) 10-9
(ii) 108
(iii) 107
(iv) 106
106

Question 25.
The periodic time of a simple pendulum is propartional to
(i) its lengths
(ii) square root of its length
(iii) reciprocal of its length
(iv) square of its length
Answer: Square root of its length.

Question 26.
One litre stands for :
(i) 103 m3
(ii) 10-3 m3
(iii) 10 m3
(iv) 100 m3
10-3 m3

Fill in the blanks

1. A scalar physical quantity can be expressed with its magnitude but _________ any direction.
without.

2. _________ physical quantities are those, each of which associates one or more fundamental physical quantities.
Derived.

3. A vector physical quantity is expressed with magnitude, proper unit as well as a _________.
direction.

4. Physical quantities are of two types, _________ and vector.
scalar.

5. Any __________ quantity related to a material body or any natural or mechanical event is known as a physical quantity.
measurable.

6. The time that elapses between two consecutive apparent transits of the Sun across the __________ at a place is known as Solar day.
meridian.

7. Dimension is a _________ or quotient of the fundamental quantities involved in a derived physical quantity raised to appropriate powers.
product.

8. Some physical quantities have no units, since each is expressed by a _________ of similiar physical quantities.
ratio.

9. Derived units are obtained by using a fundamental unit more than once or by using two or more __________ units.
fundamental.

10. Measurement of a physical quantity means to compare it with a standard physical quantity of the _________ nature accepted by all in the world.
same.

11. Spring balance measures the __________ of a body.
weight.

12. __________ is the mass per unit volume.
Density.

13. Velocity is a _________ quantity.
vector.

14. Anything that can be measured is a _________ quantity.
physical.

15. CGS system is also known as ___________ system.
metric.

16. InCGS system unit of mass is __________.
gram.

17. InCGS system, unit of density is ___________.
g/c.c.

18. Mass of 1 c.c. of pure water at 4°C is ___________.
1 g.

19. A measuring cylinder is used for measuring the volume of a _____________.
liquid.

20. The weights in the weight box are in the ratio of ___________.
5 : 2 : 2 : 1

21. Work is a ___________ quantity.
scalar.

22. 1 A° = ___________ cm.
10-8

23. The dimension of force is ____________.
[MLT-2]

24. Stopwatch has no __________ hand.
hour.

25. The light year is the unit of ____________.
distance

26. Small time intervals are measured by ___________.
stopwatch.

## WBBSE Class 9 Physical Science Solutions Chapter 3 Matter: Structure and Properties

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 3 Matter: Structure and Properties offer valuable context and analysis.

## WBBSE Class 9 Physical Science Chapter 3 Question Answer – Matter: Structure and Properties

Question 1.
What is the unit of density in SI System ?
The unit of density in SI system is : kgm-3.

Question 2.
What is the unit of specific gravity in CGS system ?
The unit of specific gravity in CGS system is : gcm-3.

Question 3.
What is fluid?
The word fluid cames from a Latin word ‘fluere’ meaning ‘to flow’.

Question 4.
Is pressure a scalar quantity ?
No, pressure is not a scalar quantity. It is a vector quantity.

Question 5.
Give the dimensional formula of pressure.
The dimensional formula of pressure is : [ML-1 T-2].

Question 6.
What is the relation between density and specific gravity of substance?
Density of a substance = specific gravity of the substance × density of water at 4°.

Question 7.
What is buoyancy?
The upward thrust which any fluid exerts upon a body partly or wholly submerged in it is called its buoyancy.

Question 8.
Does buoyancy depend on the depth of the liquid to which a body is immersed?
The buoyancy does not depend on the depth of the liquid to which the body is immersed.

Question 9.
Is there any gas in the Torricellian space?
The empty space above the mercury level in the tube contains practically nothing but a negligible amount of mercury vapour and is known as Torricellian space.

Question 10.
Will the siphon work, if there be a hole at any point in the longer arm above the surface of the liquid in the vessel in which the shorter arm is placed?
When a hole is made at any point in the longer arm above the surface of the liquid in the vessel in which the shorter arm is placed, siphon will not work.

Question 11.
Is surface tension a vector quantity ?
Surface tension is a scalar quantity as it has no specific direction.

Question 12.
What is the unit of surface energy ?
The unit of surface energy is Joule.

Question 13.
What is capillarity ?
The phenomenon of rise or fall of liquid in a capillary tube is called capillarity.

Question 14.
Define ‘angle of contact’.
The angle which the tangent to the liquid surface at the point of contact makes with the solid surface inside the liquid is called angle of contact.

Question 15.
What happens to surface tension, when impurity is mixed in it ?
The presence of impurities in the liquid surface or dissolved in it, considerably affect force of surface tension and depends on the degree of contamination.

Question 16.
How rough sea can be calmed ?
Rough sea can be calmed by pouring oil on sea water.

Question 17.
In a streamline flow, what is the velocity of the liquid in contact with the containing vessel.
Zero.

Question 18.
What is terminal velocity ?
Terminal velocity of a body is the constant maximum velocity acquired by a body while falling through a viscous fluid.

Question 19.
Can two streamline cross each other ?
No.

Question 20.
What is the terminal velocity of a body in a freely falling system?
Terminal velocity of a body in a freely falling system is zero.

Question 21.
What is the acceleration of a body falling through a viscous fluid after terminal velocity is reached?
Zero.

Question 22.
Velocity of water in a river is less on the bank and large in the middle. Explain.
Velocity of water in contact with solid banks is zero and it increases as we go towards the middle of the river.

Question 23.
The velocity of fall of a man jumping with a parachute first increases and then become constant. Why?
It is because of the fact the man attains terminal velocity.

Question 24.
What is the SI unit of coefficient of viscosity ?
The SI unit of coefficient of viscosity is Decapoise (Nsm-2).

Question 25.
What is critical velocity ?
Critical velocity : It is the velocity of flow of a liquid upto which its flow is streamlined and above which its flow becomes turbulent.

Question 26.
Does viscosity come into play if there is relative motion of the liquid layers?
Yes, it depends on the relative velocity of two layers.

Question 27.
Does viscosity depend on the area of the layers in contact ?
Viscosity depends on the area of the liquid layers.

Question 28.
What do you mean by an ideal fluid?
An ideal fluid has zero viscosity and zero compressibility.

Question 29.
Is viscosity a vector quantity ?
No, viscosity is a scalar quantity.

Question 30.
Write down the dimensional formula for coefficient of viscosity.
The dimensional formula for coefficient of viscosity is : [ML-1T-1].

Question 31.
How does the viscosity of a liquid change with the change in temperature?
The viscosity of a liquid increases with decrease in temperature and vice-versa.

Question 32.
How does the viscosity of a gas change with the change in temperature?
The viscosity of a gas increases with increase in temperature and vice-versa.

Question 33.
What is the value of Reynolds number for streamline flow ?
NR < 2000.

Question 34.
Why does air bubble in a liquid rise up ?
As terminal velocity of an air bubble is negative.

Question 35.
Is Bernoulli’s theorem valid for viscous liquid?
No.

Question 36.
Water and castor oil taken in two different flasks and shaken violently and kept on a table. Which liquid will come to rest earlier?
Castor oil having higher viscosity will come to rest earlier.

Question 37.
Out of friction force and viscous force, which one depends on velocity?
Viscous force depends on velocity, but friction force is independent of velocity.

Question 38.
The hotter liquid flows faster than colder one. Why ?
The coefficient of viscosity of liquid decreases with rise in temperature and so liquid flows faster.

Question 39.
What are the properties of a liquid satisfying Bernoulli’s theorem ?
The liquid must be ideal one.

Question 40.
What are the dimensions of stress and strain ?
Stress = [ML-1T-2] and strain = [M°L°T°]

Question 41.
What is more elastic – water or air ?
Water Bulk modulus of elasticity is reciprocal of compressibility and air is more compressible than water.

Question 42.
Why are springs made of steel and not of copper?
Modulus of elasticity of steel is more than that of copper.

Question 43.
What is the value of modulus of rigidity for a liquid ?
Zero

Question 44.
What is the value of young’s modulus for an incompressible liquid?
Zero

Question 45.
What is the unit of Poisson’s ratio?
No unit

Question 46.
What is the value of bulk modulus for an incompressible liquid ?
Infinite

Question 47.
What is more elastic – steel or rubber ?
Steel

Question 48.
What is more fundamental – stress or strain ?
Strain is more fundamental, as stress is developed only when a body is strained.

Question 49.
Is poisson’s ratio an elastic modulus ?
No. Poisson’s ratio is unitless while elastic modulus has unit Nm-2.

Question 50.
Is there any truly rigid body ?
No, there is to truly rigid body.

Question 51.
What is hydrostatic pressure?
Hydrostatic pressure : The normal force exerted by the fluid at rest per unit area of the surface in contact with it is called the pressure of fluid or hydrostatic pressure.

Question 52.
What is S.I. unit of pressure?
The S.I. unit of pressure is Nm-2 or pascal (Pa}).

Question 53.
Define thrust.
Thrust – The total normal force exerted by a fluid at rest on a surface in contact with it, is thrust.

Question 54.
What is the unit of thrust in S.I. ?
The unit of thrust is newton (N).

Question 55.
State the relationship between thrust and pressure.
Thrust = Pressure × Area.

Question 56.
When an object is immersed in a fluid, name the two forces acting on it.
Two forces are upward thrust and weight of the body.

Question 57.
Define upthrust.
When a body is immersed partly or fully in a fluid, it appears to become lighter. This occurs due to the fact that the fluid exerts an upthrust on the immersed object.

Question 58.
State Archimedes’ principle.
Archimedes’ principle : It states that a body immersed wholly or partly in a fluid at rest, appears to lose a part of its weight, which is equal to the weight of the fluid displaced.

Question 59.
Define relative density.
Relative density : Relative density of a substance is the ratio of the density of the substance to the density of pure water at 4°.

Question 60.
Define density. Give S.I. unit of density.
Density : Density of a substance is its mass per unit volume.
S.I. unit of density : Kgm-3

Question 61.
What is meant by atmosphere?
Atmosphere : The earth’s surface is surrounded by air extending upto a height of about 500 km which is called atmosphere.

Question 62.
Name the instrument used for measuring atmospheric pressure.
Barrometer is an instrument for measuring the pressure of the atmosphere.

Question 63.
What is the value of normal atmospheric pressure?
Normal atmospheric pressure is the pressure exerted by the 760 mm length of mercury column.

Question 64.
What is siphon ?
Siphon : Siphon is a simple device for transferring liquid from one vessel to the other without disturbing the whole volume of the liquid.

Question 65.
What is the unit of surface tension in SI ?
Nm-1 is the unit of surface tension in SI.

Question 66.
State whether surface tension is a scalar or vector quantity.
Surface tension is a scalar quantity as it has no specific direction.

Question 67.
What is streamlines ?
Streamlines : In streamline flow, the path of any particle of the fluid is always directed along the line of motion of the fluid and each particle in the fluid travels in exactly the same path, which is called a streamline, as the particle preceding it.

Question 68.
On what princple is Bernoulli’s theorem based?
Bernoulli’s theorem is based on the principle of conservation of energy applied to a liquid in motion.

Question 69.
What is stress ?
stress : Whenever a deforming force is applied to a body, an internal reaction force is developed in it which tends to resist the applied force and also to maintain the original shape and size of the body. The restoring force developed per unit area of the body is called stress.

Question 70.
Define strain. what is its unit?
Strain : It is the ratio of the change in length, volume or shape to the original configuration.
The strain being the ratio of two similar quantities is a pure number having no unit.

Question 71.
What is the SI unit of stress ?
SI unit of stress is dyne/cm2.

Question 72.
State Hooke’s law.
Hooke’s law : Within elastic limit, the stress developed in a body is proportional to the strain produced in it.

Question 73.
Mention one use of elasticity in our deaily life.
The metallic parts of machineries are so designed that they are not subject to possible stress beyond elastic limit.

Question 1.
A floating body loses its weight – explain.
Explanation : The weight of a floating body is equal to the weight of the liquid displaced by it. These two forces act in opposite direction along the vertical line. Thus these forces balance each other and apparently floating body loses weight.

Question 2.
Does siphon work on the surface of moon ? Explain.
Explanation: There being no atmosphere in the moon, there is no atmospheric pressure. So, siphon does not work on the moon.

Question 3.
Explain whether the rate of flow of liquid through a siphon will change if the atmospheric pressure changes.
Explanation : No. The rate of flow of liquid through a siphon depends on the differences of pressures of liquid columns in its two limbs and not on the barometric pressure.

Question 4.
Can you siphon out water from a leaking boat to the river ?
Explanation : No, the boat is floating on the river and water leaks into the boat from the river. Thus water inside the boat would be always in the same level as that of the river outside. So it is not possible to siphon out water in this case.

Question 5.
Why should a field be ploughed before sowing?
Explanation: This is done to break the tiny capillaries through which water rises and finally evaporates. The ploughing of field helps the soil to retain the moisture.

Question 6.
Explain why oil rises in the wick of a lamp?
Explanation : The pores in the wick serve the purpose of a number of line capillaries. The oil rises due to capillary action.

Question 7.
Will the rate of flow change in a siphon if water be replaced by mercury ?
No, the rate of flow of liquid in a siphon does not depend on the density of the liquid.

Question 8.
Can you use water in a barometer?
The height of water barometer would be about 10 ~m}, which is not practicable.Further water sticks to glass and water is to be coloured.

Question 9.
Why water does not wet a glass rod coated with wax ?
Because, force of adhesion between water and wax is less than the force of cohesion between water molecules.

Question 10.
Why mercury does not wet glass ?
The cohesive force between mercury molecules is greater than the adhesive force between mercury and glass.

Question 11.
Why hot soup tastes better than cold soup?
The surface tension of hot soup is less than the cold soup and thus soup spreads over larger area of the tongue.

Question 12.
Why soap bubble burst after sometime?
Soap bubbles burst when pressure inside them become more than outside atmospheric pressure. So, soap bubbles burst after sometime.

Question 13.
The diameter of a ball is twice that of another ball. What will be the ratio of the their terminal velocities in water ?
We know that, the terminal velocity is directly proportional to the square of the radius of the ball. i.e.
The terminal velocity α (radius of the ball)2
∴ ratio of their terminal velocities will be 4 : 1

Question 14.
Water is coming out of a hole made on the wall of a fresh water tank. If the size of the hole is increased, (i) will the velocity of efflux of water change? (ii) Will the volume of water coming out per second change?
(i) Velocity of efflux remains unaltered, as it depends only on the depths of the hole below the fresh surface of water.
(ii) Volume changes, as volume of the liquid flowing per second depends upon the area of cross-section of the hole.

Question 15.
Explain, why still water runs deep?
Explanation : From equation of continuity, we have, a v= constant.
The speed of still water is very small and so area would be large. Thus still water becomes deep.

Question 16.
Why does the velocity increase, when water flowing in a broader pipe enters into a narrower pipe?
From equation of continuity, we have a v = constant. So, when water enters into a narrower pipe flowing from a broader pipe, then area of cross-section decreases and thus velocity of flow increases.

Question 17.
Small air bubbles rise slower than the bigger one through a liquid, why?
The terminal velocity of a bubble is proportional to the square of the radius of the bubble. So, smaller air bubbles having smaller radii would have low values of terminal velocities and rise with slower rate.

Question 18.
Why do clouds float in the sky?
The tiny drops of water present in clouds have negligibly small terminal velocity. So, clouds float in the sky.

Question 19.
Why should the lubricant oils be of high viscosity ?
Lubricants are used for decreasing dry friction between different parts of the machines. The lubricants with high viscosity would stick to the machine parts and would not come out during movements of the machine parts.

Question 20.
Why is viscosity called internal friction?
There is a backward drag on each of the upper layer of a flowing liquid by the lower layer. So, viscosity acts like friction from within and thus it is called internal friction.

Question 21.
What is elasticity ?
Elasticity : It is the property by which a body is able to resist deformation, either in shape or in volume or both, and recovers its original configuration when the deforming force is removed.

Question 22.
What is elastic limit ?
Elastic limit : It is the upper limit of deforming force upto which the body regains its original shape or size completely or removal of deforming force and beyond which on increasing the deforming force, the body loses its property of elasticity and gets permanently deformed.

Question 23.
‘The poisson’s ratio depends only on the nature of the material and not at all on the stress applied within elastic timit’ – explain.
Poisson’s ratio = $$\frac{\text { lateral strain }}{\text { longitudinal strain }}$$
which does not involve stress within elastic limit and depends only on the nature of the material.

Question 24.
What is Hooke’s law ? What is generalised Hook’s law ?
bullet Hooke’s law : The deformation of an elastic body is directly proportional to the applied force within elastic limit.
Generalised Hooke’s law : Within elastic limit, stress is proportional to strain.

Question 25.
What is elastic fatigue?
The property of an elastic body by virtue of which its behaviour becomes less elastic under the action of repeated alternating deforming forces is called elastic fatigue.

Question 26.
What is Tensile stress ?
Tensile stress : If there be increase in length or extension of a body in the direction of the applied force, the stress developed is called tensile stress.

Question 1.
How will the reading of a mercury barometer, placed inside a lift, change if the lift starts moving downwards with a given acceleration? Give reasons for your answer.
Reason : Let the lift descend with acceleration f. Then effective acceleration with which it descends will be (g-f). Thus the weight of mercury column in the barometer decreases. But atmospheric pressure remaining the same, the height of the mercury column in the barometer would be more.

Question 2.
Why are small liquid drops spherical in shape, while big drops are flat ?
A liquid drop attains spherical shape to have minimum surface area and hence minimum potential energy state. In a small liquid drop the force due to surface tension is large compared to the force due to weight of the drop or gravitational pull and the drop attains spherical shape. But as the size of the drop increases, its weight also increases, which pulls the drop downwards and it becomes flat.

Question 3.
Water rise in a capillary tube whereas mercury falls in the same tube. Explain.
Explanation: The cohesive force between mercury molecules is much larger than the force of adhesion between mercury and glass. While the force of adhesion between water and glass is much more than the force of cohesion between water molecules.

Question 4.
Two soap bubbles of unequal sizes are blown at the ends of a capillary tube. Which one will grow at the cost of the other?
Excess of pressure p is inversely proportional to the radius r of the soap bubble i.e. p inside a small bubble will be more than that inside the large bubble. So, big bubble will grow at the cost of smaller one.

Question 5.
Oil spreads over the surface of water while does not do so on oil surface. Explain.
Explanation : Surface tension of oil is less than the surface tension of water. So on spreading oil on the surface of water, it spreads in all directions due to the higher force of surface tension of water.

Question 6.
Why does surface tension vary with temperature?
With the increase of temperature, the force of cohesion of the liquid molecules decreases. So surface tension decreases with increase of temperature.

Question 7.
Why do two mercury drops form one drop when brought in contact?
Explanation : Liquids tend to attain minimum surface area state due to surface tension. When two drops come in contact, they form a single drop for decreasing surface area.

Question 8.
Explain how a spider walks easily on the surface of water.
Explanation: The free surface of water behaves as a stretched membrane due to surface tension. This membrane is depressed due to the weight of the spider. The vertical component of the surface tension balances the weight of the spider and hence it is able to walk on the water surface.

Question 9.
A needle may float on clean water but sinks in water having detergent. explain.
Explanation : The free surface of water acts like a stretched membrane due to surface tension and a needle can float on it. But on adding some detergent, surface tension of water decreases and the tension in the membrane is weakened and it can no longer hold the weight of the needle.

Question 10.
Small pieces of camphor dance when placed on the surface of water. Why ?
Surface tension of water decreases when camphor dissolves in it. Due to its irregular shape, the camphor dissolves unevenly on different sides. So, unbalanced surface tension forces act on the camphor and hence the piece of camphor moves randomly in different directions.

Question 11.
The velocity of water in a river is less on the bank and large in the middle; why?
Explanation: The water in the river flows in the form of streams. The forces of adhesion is less on the streams in the middle of the river than near the bank. So, the velocity of streams near the bank is minimum and is maximum in the middle of the river.

Question 12.
Explain the effect of (i) density (ii) temperature (iii) pressure on the viscosity of liquids and gases.

1. With increase in density, viscosity of liquid increases, while for gases, it decreases.
2. With increase in temperature, viscosity of liquid decreases, while that of gases increases.
3. With increase in pressure, the viscosity of liquids except water increases and that of water decreases. In the case of gases viscosity is practically independent of pressure.

Question 13.
How will the weight of a body be affected, when it falls with its terminal velocity through a viscous medium?
When a body falls through a viscous medium with its terminal velocity, it moves with constant velocity. So, no resultant force is acting on the body, as pull due to gravity is balanced by viscous drag and buoyancy of medium. Hence the effective weight of the body becomes zero.

Question 14.
The stream of water flowing at high speed from a garden hose pipe tends to spread like a fountain when held vertically up, but tends to narrow down when held vertically down. Why?
As the stream falls, its speed v increases and consequently its area of cross-section, a will decrease, according to equation of continuity,
av = constant, and hence the stream becomes narrow.
When the stream goes up, its speed decreases, so, its area of crosssection increases and hence it becomes broader and spreads out like a fountain.

Question 15.
It is advised not to stand near a running train. Why ?
When a fast moving train passes on a rail, the velocity of streams of air between the rail and the man standing near the rail will be larger than the velocity of air streams on the other side of the man away from the rail. Following Bernoulli’s theorem, the pressure of air will be low in between the man and the rail and high on the other side of the man. Thus the man may be pushed towards the rail and may meet with an accident.

Question 16.
Define stress and strain. Give their units.
Stress : Whenever a deforming force is applied to a body, internal force of reaction comes into play, which tends to resist the deforming force and maintains the original configuration of the body. This reaction force developed per unit area of the body is called stress.
Units of stress : (i) CGS unit : dyne cm-2 (ii) SI unit : Nm-2
Strain : When a deforming force is applied on a body, there is a change in the configuration of the body and the body is said to be strained i.e., the strain is the measure of the amount of deforming produced in the body.
unit of strain : (i) CGS : No unit (ii) SI : No unit [Strain being the ratio of two like quantities has no unit ]

Question 17.
Define longitudinal stress. What is its unit in (i) CGS system (ii) SI system ?
Longitudinal Stress : If there be increase in length or extension of a body in the direction of the applied force, the stress developed is called longitudinal stress.
Unit of longitudinal stress : (i) CGS : dyne cm-2 (ii) SI : Nm-2

Question 18.
State and Explain Hooke’s law.
Hooke’s Law : The deformation of an elastic body is directly proportional to the applied force within elastic limit.
Afterfwards English scientist Thomas Young modified the law to a general form and is known as generalised Hooke’s law.
This is stated as :
Within elastic limit, stress is proportional to strain. Thus, within elastic limit, stress α strain
$$\text { or, } \frac{\text { stress }}{\text { strain }}=\text { constant }$$
This proportionality constant is known as coefficient of elasticity or modulus of elasticity of a body which is independent of magnitude of stress and strain but depends upon the nature of the material of the body and the way in which the body is deformed.

Question 19.
Define : (i) young’s modulus (ii) Bulk modulus (iii) Modulus of rigidity (iv) Poisson’s ratio.
(i) Young’s modulus : Young’s modulus of elasticity is the ratio of the longitudinal stress to the longitudinal strain within the elastic limit.
(ii) Bulk modulus : Bulk modulus of elasticity is the volume stress (normal stress) to the volume strain within elastic limit.
(iii) Modulus of rigidity : Modulus of rigidity or shear modulus of a material is the ratio of the shearing stress to the shearing strain within elastic limit.
(iv) Poisson’s ratio : The ratio of the lateral strain to longitudinal strain of the material of a wire or bar under tension is called its poisson’s ratio.

Numerical Problems

Working formula :

(i) D = $$\frac{m}{v}$$ (D = density, m = mass, v = volume)
(ii) P = $$\frac{F}{A}$$ (P = Pressure, F = normal force, A = Area)
(iii) P = h d g(P = Pressure, d = density, g = acceleration due to gravity)
(iv) T = $$\frac{F}{l}$$ (F = the total force acting as an imaginary line of length l, drawn tangentially on the liquid surface at rest, the force of surface tension T)
(v) E = T × a (E = Surface energy, T = Surface tension, a = area)
(vi) P = $$\frac{2T}{R}$$ (P = excess of pressure inside the liquid drop,
T = surface tension of the liquid,
R} = radius of the water drop)
(vii) Stress = $$\frac{\text { external deforming force on the body }}{\text { area of cross-section of the body }}$$
(viii) $$\frac{\text { Stress }}{\text { Strain }}$$ = constant
(ix) Poisson’s ratio = $$\frac{\text { lateral strain }}{\text { longitudinal strain }}$$
(x) $$\frac{P}{\rho g}+h+\frac{v^2}{2 g}$$ = constant (For the streamline flow of an ideal fluid of density \rho and passing any cross-section at a height h with a velocity v at pressure P and acceleration due to gravity is g)
(xi) Excess pressure inside a soap bubble (P) =
$$\frac{4 T}{R}$$(T = surface tension of liquid R = radius of the liquid bubble)
(xii) F = $$\frac{Y a l}{L}$$
(F = external tensile force, Y = longitudinal stress, L = length of wire ; a = cross-section, l = elongated by length)

Example 1 : A water filled cone of height 50 cm and the base area of 20 cm 2 is placed on a table with the base on the table. What is the thrust offered by the water on the table?
h = 50 cm
d = 1 gcm-3
g = 980 cms-2
A = 20 cm2
Thrust = Pressure × area = h d g × A
∴ Thrust
= 50 × 1 × 980 × 20
= 9.8 × 105 dyne
= 9.8 N

Example 2 : The pressure of air in a soap bubble of 0 . 7 cm diameter is 8 mm of water above the atmospheric pressure. Calculate the surface tension of the soap solution.
P = 8 mm = 0.8 cm
r = 0.7 cm / 2 = 0.35 cm
The excess of pressure inside a soap bubble is given by
P = $$\frac{4 T}{r}$$
∴ T = $$\frac{P r}{4}$$
= $$\frac{0.8 × 980 × 0.35}{4}$$
= 686 dyne cm-1

Example 3: Surface tension of water is 0.072 Nm-1. Calculate the excess pressure inside a water drop of diameter 1.2 mm.
T = 0.072 Nm-1
d = 1.2 mm = 1.2 × 10-3 m
P = $$\frac{2 T}{r}$$ = $$\frac{4 T}{d}$$
= $$\frac{4 \times 0 \cdot 072}{1.2 \times 10^{-3}}$$
= $$\frac{4 × 0.072}{1 . 2 × 10^{-3}}$$
= 240 Nm-2

Example 4 : one end of an iron wire of length 250 cm of diameter 1 mm is rigidly fixed with a beam and a weight of 8 kg} is placed at the other end. Calculate the elongation of the wire.
(Y. of iron = 20 × 1011 dyne cm-2 ; g = 9.8 ms-2)
L = 250 cm = 2.5 m
d = 1 mm = 10-3m
W = 8 kg . wt
Y = 20 × 1011 dyne cm-2
= 2.0 × 1011 Nm-2
g = 9.8 ms-2
l = ?
l = $$\frac{F L}{A}$$

= 0.125 × 10-2 m

Example 5 : Find the pressure at a depth of 5 m below the surface of a lake. (Density of water = 1000 kgm-3).
h = 5 m
d = 1000 kgm-3
g = 9.8 ms-2
p = ?
P = hdg
P = 5 × 1000 × 9.8
Or,
= 4.9 × 104 Nm-2

Example 6 : Atmospheric pressure at a place is 750 mm. Find the pressure at the place. (Given density of mercury = 13.6 g / cc and g = 980 cm/s2)
h = 750 mm = 75 mm
d = 13.6 g / cc
g = 980 cm / s2
p = ?
P = hdg
= 75 × 13.6 × 980
= 0.9995 × 106 dyne/cm2

Example 7 : A body having volume of 50 cm 3 weighs 0.5 kg in air. Find its density.
m = 0.5 kg
v = 50 cm
= 50 × 10-6 m3
D = ?
Density of the body (D) = $$\frac{m}{v}$$
= $$\frac{0.5}{50 × 10^{-6}}$$
= 104 kgm-3

Example 8 : Relative density of silver is 10.5 Find the density of silver.
Given, relative density of silver = 10.5
Now, relative density of silver = $$\frac{\text { density of silver }}{\text { density of water }}$$
∴ density of silver
= relative density of silver × density of water
= 10.5 × 1000 = 10500 kgm-3

Example 9 : A block of 36 cc. ice floats on water. What volume of it remains above water surface?
It is known that nearly $$\frac{1}{12}$$ part of the volume of an ice block remains above water when it floats on water.
Here total volume of the ice block is 36 cc.
∴ $$\frac{1}{12}$$ of 36 cc = 3 cc
So, 3 cc of ice remains above water surface.

Example 10 : Gold has density 19.3 g/cc. An ornament weighs 5.80 g in air and 5.25 g in water. Is the ornament made of pure gold ?
From Archimedes’ principle we get, volume of the ornament = (5.80 – 5.25) cc = 0.55 cc.
Now, considering density of pure gold 19.3 g / cc, the weight of the ornament in air = (19.3 × 0.55) g-wt. = 10.615 wt. But as indicated in the problem, weight of the ornament in air is 5.80 g-wt. Hence, the ornament is not made of pure gold.

Example 11 :
A metallic wire of length 60 cm when stretched along length by a normal force becomes 61 cm Find the longitudinal strain.
Given, original length of wire, l = 60 cm
final length of the wire, l’ = 61 cm
increase in length Δ l = l’-1 = (61-60)
cm = 1
∴ longtudinal strain = $$\frac{\Delta l}{l}$$ = $$\frac{1}{60}$$ = 0 . 017

Example 12 : A metallic wire of radius 0.1 cm and length 2 m is extended by a weight of 2.5 kg. Find the normal stress set up.
Given external deforming
force, F = 2.6 kg-wt = 2.5 × 9.8 N
radius of the wire, r = 0 . 1 cm
= 0.1 × 10-2 m
area of cross-section of the wire = π r2 = π(10-3)2 m2
Since normal stress = $$\frac{\text { external deforming force }}{\text { area }}$$
= $$\frac{2.5 × 9.8}{\pi(10^{-3})^2}$$
= 7.8 × 106 Nm-2

Example 13 :
The ratio radiis of two wires of same material is 2: 1. If these wires are stretched by equal force, find the ratio of stresses produced in them.
Given r1: r2 = 2 : 1
F1 = F2 = F
Stress (S) = $$\frac{\text { force }}{\text { area }}$$ = $$\frac{F}{\pi \sigma^2}$$ or, s α $$\frac{1}{r^2}$$
∴ $$\frac{S_1}{S_2}$$ = $$\frac{r_2^2}{r_1^2}$$ = $$(\frac{1}{2})^2$$ = $$\frac{1}{4}$$

## WBBSE Class 9 Physical Science MCQ Questions Chapter 4.2 Mole Concept

Well structured WBBSE Class 9 Physical Science MCQ Questions Chapter 4.2 Mole Concept can serve as a valuable review tool before exams.

## Mole Concept Class 9 WBBSE MCQ Questions

Multiple Choice Questions :

Question 1.
Which scientist first gave the concept of molecule ?
(i) Dalton
(iii) Berzelius
(iv) Boyle

Question 2.
What is the volume of 1 gram-molecule of a gas or vapour at NTP ?
(i) 22.4 ml
(ii) 22.4 lit
(iii) 1000 ml
(iv) 2.24 lit
22.4 lit

Question 3.
In the reaction, N2 + 3H2 = 2NH3, the ratio of volumes of nitrogen, hydrogen and ammonia is 1 : 3 : 2. These figures illustrate the law of :
(i) constant proportion
(ii) multiple proportion
(iii) reciprocal proportion
(iv) Gay Lussac’s law of gaseous volumes
Gay Lussac’s law of gaseous volumes

Question 4.
At NTP, 5.6 lit of a gas weigh 8 grams. The vapour density of the gas is :
(i) 32
(ii) 40
(iii) 16
(iv) 8
16

Question 5.
Which of the following contains the least number of molecules ?
(i) 1g H2
(ii) 2g N2
(iii) 4g O2
(iv) 11g CO2
2g N2

Question 6.
Which of the following volume of the gas at NTP contains the largest number of molecules?
(i) 200 ml H2
(ii) 100 ml O2
(iii) 150 ml N2
(iv) 22.5 ml NH3
200ml H2

Question 7.
One of the following statements is not applicable to 1 mole of carbon dioxide :
(i) 22g CO2
(ii) 22.4 lit of the gas
(iii) 1 gram atom of carbon and 2 gram atoms of oxygen
(iv) 6.023 × 1023 molecules of carbon dioxide
22g CO2

Question 8.
A mole of any gas :
(i) always occupies one litre
(ii) always occupies 22.4 lit at NTP
(iii) can occupy any volume at NTP
(iv) always occupies 11.2 lit at NTP
Always occupies 22.4 lit at NTP

Question 9.
The latest standard of atomic weight is :
(i) Hydrogen = 1
(ii) Oxygen = 16
(iii) Carbon = 12
(iv) Nitrogen = 14
Carbon = 12

Question 10.
The approximate number of molecules in 4.25 g of ammonia is :
(i) 1.0 × 1023
(ii) 1.5 × 1023
(iii) 2.0 × 1023
(iv) 3.5 × 1023
1.5 × 1023

Question 11.
Atomic weight of chlorine is 35.5 . It has two isotopes of atomic weight 35 and 37 . What is the percentage of the heavier isotope in the sample?
(i) 5
(ii) 25
(iii) 20
(iv) 15
25

Question 12.
Number of molecules in one litre of water, is close to :
(i) $$\frac{6.023}{23.4}$$ × 1023
(ii) 18 × 6.023 × 102
(iii) $$\frac{18}{22.4}$$ × 1023
(iv) 55.5 × 6.023 × 1023
55.5 × 6.023 × 1023

Question 13.
Volume at NTP of 0.22 g of CO2 is the same as that of
(i) 0.01 g of H2
(ii) 0.085 g of NH3
(iii) 320 mg of gaseous SO2
(iv) All of the above
All of the above

Question 14.
Avogadro’s number of helium atoms weighs :
(i) 1 g
(ii) 4 g
(iii) 8 g
(iv) 4 × 6.023 × 1023 g
4 g

Question 15.
The molecular mass of CO2 is 44 amu. Avogadro’s number is 6.023 × 1023, therefore the mass of one molecule of CO2 is :
(i) 7.31 × 10-23
(ii) 3.65 × 10-23
(iii) 1.01 × 10-23
(iv) 2.01 × 10-23
7.31 × 10-23

Question 16.
4.0 grams of caustic soda contains :
(i) 6.023 × 1023 atoms of hydrogen
(ii) 4 g} atoms of sodium
(iii) 6.023 × 1022 atoms of sodium
(iv) 4 moles of caustic soda
6.023 × 1022 atoms of sodium

Question 17.
Which of the following weighs the least ?
(i) 24g of magnesium
(ii) 0.9 moles of nitric oxide
(iii) 22.4 lit of N2
(iv) 6.023 × 1024 molecules of oxygen
24g of magnesium

Question 18.
One mole of CO2 contains :
(i) 6.023 × 1023 atoms of carbon
(ii) 6.023 × 1023 atoms of oxygen
(iii) 18.1 × 1023 molecules of carbon dioxide
(iv) 3 gram atoms of carbon dioxide.
6.023 × 1023 atoms of carbon

Question 19.
One amu is :
(i) 1.00748 g
(ii) 0.000549 g
(iii) 1.66 × 10-24 g
(iv) 6.023 × 10-23 g
1.66 × 10-24 g

Question 20.
The vapour density of a gas is 11.2. The volume occupied by 11.2 g of the gas at NTP is :
(i) 1 L
(ii) 11.2 L
(iii) 22.4 L
(iv) 10 L
11.2 L

Question 21.
The vapour density of pure ozone would be :
(i) 16
(ii) 24
(iii) 32
(iv) 48
24

Question 22.
At STP 5.6 lit of a gas weighs 60g. The vapour density of the gas is :
(i) 30
(ii) 60
(iii) 120
(iv) 240
120

Question 23.
The largest number of molecules is in :
(i) 34 g water
(ii) 54 g oi CO2
(iii) 46 g of CH3 OH
(iv) 54 g of N2 O5
34g water

Question 24.
The number of oxygen atoms in 4.4 g of CO2 is approx:
(i) 1.2 × 1023
(ii) 6 × 1023
(iii) 6 × 1022
(iv) 12 × 1023
1.2 × 1023

Question 25.
The number of molecules in 16g of methane (CH4) is :
(i) 3.0 × 1023
(ii) 6.023 × 1023
(iii) $$\frac{16}{6.023}$$ × 1023
(iv) $$\frac{16}{3}$$ × 1023
6-023 × 1023

Question 26.
0.56 g of a gas occupies 280 ml at NTP, then its molecular mass is :
(i) 4.8
(ii) 44.8
(iii) 2
(iv) 22.4
448

Question 27.
‘Mole’ means
(i) a molecule
(ii) number of molecules
(iii) number of atoms
(iv) avogadro’s number of any particle

Question 28.
0.012 kg2 C-12 isotope contains howmany C-12 atoms ?
(i) 12
(ii) 6.022 × 1023
(iii) 1.66 × 10-24 g
(iv) 12 g atom.
6.022 × 1023

Question 29.
(i) Chemistry only
(ii) Physics only
(iii) Biology only
(iv) Chemistry, Physics and biology
Chemistry, physics and biology.

Question 30.
The value of Avogadro’s number is :
(i) 6.320 × 1023
(ii) 6.022 × 1023
(iii) 6.320 × 1023
(iv) 6.029 × 1023
6.022 × 1023

Question 31.
Formula unit mass of KCl is :
(i) 57.4 U
(ii) 45.7 U
(iii) 49.8 U
(iv) 74.5 U
74.5 U

Fill in the blanks :

1. Equal volumes of all gases under the same condition of temperature and pressure contain the same number of _______ .
molecules

2. Atomic weight of an element expressed in gram is called its ______ atomic weight.
gram

3. Avogadro’s number is ______ which is the fixed number of constituent particles present in 1 gram-molecule or in 1 gram or in 1 gram ion of any substance.
6.023 × 1023

4. Normal density = ______ density of a gas at NTP × 0.089
Vapour

5. Molecular weight of a gas = _______ × vapour density:
2

6. The gram-molecular volume of any gas or vapour occupies ______ litres at NTP.
22.4 lit

7. Molecules of elementary gases are ______.
diatomic

8. Molar volume is the volume of gram-molecular ______ of an element or a compound.
weight

9. The molecular mass of sulphuric acid is _______.
98

10. 22.4 litres of hydrogen at STP contain ______ number of hydrogen molecules.
6.023 × 1023

11. ______ was the first scientist who introduced the term molecule to indicate the smallest particle of both elements and compounds.

12. 2g of hydrogen and 32g of oxygen contain the _______ number of molecules.
same

13. The number of molecules contained in 8g of oxygen is ______.
1.505 × 1023

14. The molecular weight of chlorine is 71 . Clearly, 6.023 × 1023 atoms of chlorine weighs ______ grams.
35.5

15. The gram atoms contained in 5 g of calcium are ______.
0.125

16. The number of atoms present in 16 g of oxygen is ______.
6.023 × 1023

17. The number of gram moles present in 7g of CO is _______.
3.0115 × 1023

18. Only one atom of carbon is available from _______ of carbon.
12u

19. Between (i) 36g of H2O and (ii) 46g of nitrogen dioxide, the larger number of molecules is in ______.
36g H2O

20. The number of moles present in 90.0 g} of water is ______.
5

21. Modern atomic weights of elements are based on _____.
126 C

22. The volume occupied by 2g H2 and 32g O2 at STP is ______ cm3.
22400

23. The value 6.0233 × 1023 mol-1 is assigned to ______ constant.

24. The mass of one mole molecules of any substance is equal to ______.
Gram molecular mass

25. 12U of carbon contains how many atom of carbon.