States of Matter, Kinetic Particle Theory, Diffusion and Separation Techniques

1. A sealed syringe contains 40 cm³ of dry air at room temperature. The plunger is pushed in slowly until the volume becomes 20 cm³. The temperature remains constant.

Which statement is correct?

A The particles move twice as fast and collide with the walls twice as often.
B The particles become smaller and so occupy less space.
C The particles collide with the walls more frequently, increasing the pressure.
D The particles are forced closer together until the air becomes a liquid.

2. A liquid is heated steadily. Its temperature remains constant for several minutes even though heating continues.

Which explanation is correct?

A The particles stop moving during boiling.
B Energy is being used to overcome attractive forces between particles.
C Energy is being released as bonds form between particles.
D The liquid is pure only if the temperature continues to rise.

3. A student says that evaporation and boiling are the same because both produce gas.

Which statement correctly identifies the error?

A Evaporation occurs only at the boiling point; boiling occurs at all temperatures.
B Evaporation occurs at the surface; boiling occurs throughout the liquid.
C Evaporation releases energy; boiling absorbs energy.
D Evaporation requires impurities; boiling requires a pure liquid.

4. Four gases are at the same temperature and pressure.

Gas W has Mr 16.
Gas X has Mr 28.
Gas Y has Mr 32.
Gas Z has Mr 44.

Which order shows the gases from fastest diffusion to slowest diffusion?

A W, X, Y, Z
B Z, Y, X, W
C W, Y, X, Z
D X, W, Y, Z

5. A mixture contains sand, sodium chloride and iodine. Which sequence can separate all three substances?

A Add water, filter, crystallise filtrate, sublime residue
B Sublime, add water to residue, filter, crystallise filtrate
C Add ethanol, filter, evaporate filtrate, crystallise residue
D Distil mixture, filter distillate, sublime residue

6. Two colourless liquids have boiling points of 78°C and 82°C. They mix completely.

Which method is most suitable to separate them?

A filtration
B simple distillation
C fractional distillation
D crystallisation

7. Which statement about a gas is correct?

A Its particles vibrate about fixed positions.
B Its particles have no forces between them under all conditions.
C Its particles move randomly and collide with each other and the container walls.
D Its particles have fixed volume because they are packed closely together.

8. A pure solid is heated from 20°C to 120°C. It melts at 60°C and boils at 100°C.

At 60°C, which statement is correct?

A Only solid particles are present.
B Only liquid particles are present.
C Solid and liquid particles are present.
D Liquid and gas particles are present.

9. Which physical changes are both exothermic?

A melting and boiling
B freezing and condensation
C evaporation and sublimation
D boiling and condensation

10. A student places a crystal of potassium manganate(VII) at the bottom of a beaker of water. The purple colour slowly spreads.

Which statement best explains this observation?

A Water molecules move from high concentration to low concentration.
B Potassium manganate(VII) particles diffuse from high concentration to low concentration.
C Potassium manganate(VII) particles dissolve because they are lighter than water.
D The purple colour spreads because convection cannot occur in liquids.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. A sample of wax softens gradually between 48°C and 56°C.

What does this suggest?

A The wax is a pure compound.
B The wax is an impure substance or mixture.
C The wax is undergoing sublimation.
D The wax has no melting point.

12. A mixture contains ethanol, water and dissolved copper(II) sulfate. Ethanol boils at 78°C and water boils at 100°C.

Which process would obtain ethanol first from the mixture?

A filtration
B crystallisation
C fractional distillation
D chromatography

13. Which row correctly describes particles during condensation?

	distance between particles	energy change
A	increases	energy absorbed
B	increases	energy released
C	decreases	energy absorbed
D	decreases	energy released

14. A gas jar of hydrogen is placed mouth-to-mouth with a gas jar of carbon dioxide. After some time, both gases are found in both jars.

Which conclusion is correct?

A Only hydrogen diffuses because it is lighter.
B Only carbon dioxide diffuses because it is denser.
C Both gases diffuse because their particles move randomly.
D The gases react because they are in contact.

15. A mixture contains two solids, X and Y. X dissolves in water. Y does not dissolve in water. X decomposes when heated strongly.

Which method should be used to obtain dry solid X?

A Heat the mixture strongly and collect the residue.
B Add water, filter, then evaporate the filtrate to dryness using strong heat.
C Add water, filter, then crystallise the filtrate by gentle evaporation and cooling.
D Add water, decant the solid, then sublime the residue.

16. Which statement about diffusion is correct?

A Diffusion can occur only in gases.
B Diffusion is faster at lower temperatures because particles are closer together.
C Diffusion occurs because particles move randomly.
D Diffusion is the movement of particles from low concentration to high concentration.

17. A student separates ink using paper chromatography. The solvent front moves 12.0 cm. A dye spot moves 7.2 cm.

What is the Rf value of the dye?

A 0.40
B 0.60
C 1.67
D 4.80

18. Which pair of substances could be separated by using a separating funnel?

A ethanol and water
B sand and water
C oil and water
D sodium chloride and water

19. A student wants to obtain pure water from seawater.

Which method is most suitable?

A crystallisation
B filtration
C simple distillation
D chromatography

20. A solid changes directly into a gas when heated.

Which statement is correct?

A The process is condensation and is exothermic.
B The process is sublimation and is endothermic.
C The process is evaporation and is exothermic.
D The process is freezing and is endothermic.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21. Four substances have these melting and boiling points.

substance	melting point / °C	boiling point / °C
W	-15	60
X	25	110
Y	90	250
Z	-80	-10

Which substances are liquids at 30°C?

A W and X only
B X and Y only
C W, X and Y
D Z only

22. Which observation shows that a liquid is pure?

A It evaporates at room temperature.
B It boils over a range of temperatures.
C It boils at a fixed temperature.
D It leaves a solid residue after evaporation.

23. Which statement about the particles in a solid is correct?

A They are arranged randomly and move freely.
B They vibrate about fixed positions.
C They have no kinetic energy.
D They move from high concentration to low concentration.

24. A student heats hydrated copper(II) sulfate crystals and obtains a white powder and steam. The steam condenses on a cooler surface.

Which changes occur?

A evaporation followed by freezing
B boiling followed by melting
C vaporisation followed by condensation
D sublimation followed by crystallisation

25. Which separation method depends mainly on different solubilities of substances in a solvent and different attractions to a stationary phase?

A filtration
B fractional distillation
C paper chromatography
D decanting

26. A mixture contains powdered iron, sulfur and sodium chloride.

Which sequence could separate all three?

A Add water, filter, evaporate filtrate, use magnet on residue
B Use magnet, add water to remaining mixture, filter, evaporate filtrate
C Heat strongly, add water, filter, evaporate filtrate
D Add water, use magnet on filtrate, crystallise residue

27. A gas is cooled at constant pressure until it becomes a liquid.

Which statement is correct?

A The particles gain kinetic energy.
B The particles become further apart.
C Attractive forces become more effective as particles move more slowly.
D The particles stop moving completely.

28. Two substances have the same boiling point but different solubilities in water. One is soluble, the other is insoluble.

Which method is most suitable to separate them if they are mixed as solids?

A fractional distillation
B filtration after adding water
C paper chromatography
D simple distillation

29. A student says, “The smell of perfume reaches across a room because perfume particles are carried only by air currents.”

Which evidence best challenges this statement?

A Perfume smell spreads faster when the room is warmer.
B Perfume is a liquid before it evaporates.
C Perfume has a low boiling point.
D Perfume contains more than one substance.

30. Which statement about melting is correct?

A Melting is exothermic because particles form stronger forces.
B Melting is endothermic because particles overcome some attractive forces.
C Melting is exothermic because particles move more slowly.
D Melting is endothermic because new chemical bonds form.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31. A mixture of two dyes gives two spots on a chromatogram. Dye X has Rf 0.25 and dye Y has Rf 0.75. The solvent front moves 16 cm.

How far apart are the two spots?

A 4 cm
B 8 cm
C 12 cm
D 16 cm

32. Which condition increases the rate of diffusion of a gas?

A decreasing temperature
B increasing relative molecular mass
C increasing temperature
D changing the gas into a liquid

33. A student tries to separate a mixture of chalk powder and water by evaporation.

Why is filtration better?

A Chalk has a lower boiling point than water.
B Chalk is insoluble and can be trapped by filter paper.
C Chalk dissolves and crystallises on cooling.
D Water cannot evaporate from a mixture.

34. Which statement about liquids is correct?

A Liquid particles are fixed in a regular lattice.
B Liquid particles are far apart and move randomly at high speeds.
C Liquid particles are close together but can move past each other.
D Liquid particles have no forces of attraction between them.

35. A substance is placed in a closed container. Its particles are far apart and fill the container.

Which statement must be correct?

A The substance is a gas.
B The substance is boiling.
C The substance is pure.
D The substance is undergoing diffusion.

36. A mixture contains water, ethanol and small pieces of glass.

Which sequence is most suitable to obtain ethanol?

A filter, then fractional distillation of the filtrate
B crystallise, then filter
C use separating funnel, then evaporate
D sublime, then condense

37. A student uses chromatography to test a food colouring. The chromatogram shows one spot only.

Which conclusion is safest?

A The food colouring is definitely pure.
B The food colouring contains only one coloured substance in that solvent system.
C The food colouring contains no dissolved substances.
D The food colouring has the same Rf value in all solvents.

38. Which change involves particles becoming more ordered?

A boiling
B evaporation
C melting
D freezing

39. A student wants to separate a soluble salt from an insoluble impurity.

Which sequence is correct?

A dissolve, filter, crystallise
B filter, dissolve, crystallise
C crystallise, filter, dissolve
D dissolve, crystallise, filter before crystals form

40. Which statement about the boiling point of a liquid is correct?

A Impurities always lower the boiling point.
B A pure liquid boils over a range of temperatures.
C Boiling occurs when particles throughout the liquid have enough energy to form gas bubbles.
D Boiling happens only at the surface of the liquid.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. Four gases have the same volume at the same temperature and pressure.

Which gas contains the greatest number of particles?

A hydrogen
B nitrogen
C carbon dioxide
D all contain the same number

42. A solid has a sharp melting point and leaves no residue when melted.

Which statement is most likely?

A The solid is pure.
B The solid is a mixture.
C The solid is insoluble.
D The solid is hydrated.

43. A liquid mixture contains a dissolved solid. The liquid is flammable and boils at 56°C. The solid does not decompose.

Which method obtains the liquid safely?

A evaporating the mixture over a Bunsen burner
B filtering the mixture
C distilling the mixture using an electric heater or water bath
D crystallising the mixture to dryness

44. Which statement about sublimation is correct?

A Particles change from gas to liquid without becoming solid.
B Particles change from solid to gas without becoming liquid.
C Particles change from liquid to gas only at the boiling point.
D Particles change from gas to solid only at room temperature.

45. A student separates two dyes by chromatography. Both dyes move the same distance in solvent P but different distances in solvent Q.

Which conclusion is correct?

A Chromatography can never separate these dyes.
B Solvent Q is more suitable for separating these dyes.
C Solvent P is more suitable because both dyes have the same Rf value.
D The dyes must be the same substance.

46. A gas diffuses through a porous barrier. Its rate of diffusion is slower than methane but faster than carbon dioxide.

Which gas could it be?

A ammonia, NH3
B oxygen, O2
C sulfur dioxide, SO2
D hydrogen, H2

47. A sample of solid naphthalene is heated gently. A gas forms and then solid crystals appear on a cooler part of the apparatus.

Which pair of processes occurs?

A melting then freezing
B sublimation then deposition
C evaporation then condensation
D boiling then crystallisation from solution

48. Which statement explains why liquids are almost incompressible?

A Their particles have no spaces between them at all.
B Their particles are close together, so pressure cannot greatly reduce their volume.
C Their particles are fixed in position and cannot move.
D Their particles move rapidly in straight lines.

49. A mixture of salt and water is heated until half the water has evaporated. The remaining solution is cooled and crystals form.

Why does crystallisation occur?

A The salt decomposes at lower temperature.
B The solubility of the salt decreases as the solution cools.
C The water becomes insoluble in salt.
D The salt changes into an insoluble element.

50. Which row correctly matches the separation method with the property used?

	method	property used
A	filtration	different boiling points
B	crystallisation	different particle sizes only
C	fractional distillation	different boiling points
D	chromatography	different melting points

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1. C

A wrong: Same temperature means average kinetic energy/speed does not double.
B wrong: Particles do not become smaller.
C right: Smaller volume means particles collide with container walls more frequently, so pressure increases.
D wrong: Air does not become liquid just by this small compression at room temperature.

2. B

A wrong: Particles do not stop moving.
B right: During boiling, energy is used to overcome attractive forces between particles, so temperature stays constant.
C wrong: Energy is absorbed, not released.
D wrong: A pure liquid boils at a constant temperature, not a rising temperature.

3. B

A wrong: Evaporation occurs below boiling point too.
B right: Evaporation happens only at the surface; boiling happens throughout the liquid.
C wrong: Both evaporation and boiling are endothermic.
D wrong: Neither requires impurities.

4. A

A right: Lower Mr means faster diffusion, so 16, 28, 32, 44 gives W, X, Y, Z.
B wrong: This is slowest to fastest.
C wrong: X, Mr 28, diffuses faster than Y, Mr 32.
D wrong: W should be fastest, not X.

5. B

A wrong: If water is added first, iodine remains mixed with sand and is harder to separate cleanly.
B right: Iodine sublimes first. Then salt dissolves in water, sand is filtered off, and salt is crystallised.
C wrong: Ethanol is unnecessary and may dissolve substances unpredictably.
D wrong: Distillation is not the correct first step for this solid mixture.

6. C

A wrong: Filtration separates insoluble solid from liquid, not two miscible liquids.
B wrong: Simple distillation is poor for liquids with close boiling points.
C right: Fractional distillation separates miscible liquids with close boiling points.
D wrong: Crystallisation separates dissolved solids from solutions.

7. C

A wrong: Solids vibrate about fixed positions.
B wrong: Gases have weak forces, but not “no forces under all conditions.”
C right: Gas particles move randomly and collide with walls and each other.
D wrong: Gases do not have fixed volume.

8. C

A wrong: At melting point, solid is changing into liquid.
B wrong: Not only liquid yet.
C right: At the melting point, solid and liquid coexist.
D wrong: Liquid and gas coexist at boiling point, not melting point.

9. B

A wrong: Melting and boiling are endothermic.
B right: Freezing and condensation release energy.
C wrong: Evaporation and sublimation absorb energy.
D wrong: Boiling is endothermic, condensation is exothermic.

10. B

A wrong: The coloured particles, not water particles, explain the purple spread.
B right: Dissolved potassium manganate(VII) particles diffuse from high concentration to low concentration.
C wrong: It is not because particles are “lighter.”
D wrong: Diffusion can occur in liquids.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. B

A wrong: A pure substance has a sharp melting point.
B right: Melting over a range suggests impurity or mixture.
C wrong: Sublimation is solid directly to gas.
D wrong: It still has a melting range.

12. C

A wrong: Filtration cannot separate ethanol from water or dissolved copper(II) sulfate.
B wrong: Crystallisation obtains the dissolved solid, not ethanol.
C right: Fractional distillation separates ethanol from water because ethanol has the lower boiling point.
D wrong: Chromatography separates small samples of dissolved substances, not bulk liquids.

13. D

A wrong: Condensation brings particles closer, not further apart.
B wrong: Distance does not increase.
C wrong: Energy is released, not absorbed.
D right: Gas changes to liquid; particles become closer and release energy.

14. C

A wrong: Carbon dioxide also diffuses.
B wrong: Hydrogen also diffuses.
C right: Both gases diffuse because particles move randomly.
D wrong: Diffusion does not mean reaction.

15. C

A wrong: X decomposes on strong heating.
B wrong: Evaporating to dryness using strong heat may decompose X.
C right: Dissolve X, filter Y, then gently evaporate and cool to crystallise X.
D wrong: Sublimation is irrelevant.

16. C

A wrong: Diffusion occurs in gases and liquids.
B wrong: Diffusion is faster at higher temperatures.
C right: Diffusion happens due to random movement of particles.
D wrong: Diffusion is from high concentration to low concentration.

17. B

Rf = distance moved by spot / distance moved by solvent front
Rf = 7.2 / 12.0 = 0.60

A wrong: 0.40 uses the wrong ratio.
B right: 0.60 is correct.
C wrong: 1.67 is solvent distance / spot distance.
D wrong: 4.80 is not the correct calculation.

18. C

A wrong: Ethanol and water are miscible.
B wrong: Sand and water need filtration.
C right: Oil and water are immiscible liquids, so a separating funnel works.
D wrong: Sodium chloride dissolves in water.

19. C

A wrong: Crystallisation obtains salt, not pure water.
B wrong: Filtration cannot remove dissolved salts.
C right: Simple distillation evaporates and condenses pure water.
D wrong: Chromatography is not used to obtain pure water from seawater.

20. B

A wrong: Condensation is gas to liquid.
B right: Sublimation is solid directly to gas and absorbs energy.
C wrong: Evaporation is liquid to gas.
D wrong: Freezing is liquid to solid.

21. A

W: -15 < 30 < 60, so liquid.
X: 25 < 30 < 110, so liquid.
Y: 30 is below its melting point, so solid.
Z: 30 is above its boiling point, so gas.

A right: W and X only.
B wrong: Y is solid.
C wrong: Y is not liquid.
D wrong: Z is gas.

22. C

A wrong: Many liquids evaporate at room temperature; this does not prove purity.
B wrong: Boiling over a range suggests impurity.
C right: A pure liquid boils at a fixed temperature.
D wrong: A residue suggests impurities or dissolved solids.

23. B

A wrong: This describes a liquid or gas more than a solid.
B right: Solid particles vibrate about fixed positions.
C wrong: Solid particles still have kinetic energy.
D wrong: That describes diffusion, not solid particle arrangement.

24. C

A wrong: Steam condensing is not freezing.
B wrong: Steam forming is not melting.
C right: Water is vaporised from the crystals, then condenses on a cooler surface.
D wrong: This is not sublimation.

25. C

A wrong: Filtration depends on particle size and insolubility.
B wrong: Fractional distillation depends on boiling points.
C right: Chromatography depends on solubility in solvent and attraction to stationary phase.
D wrong: Decanting separates liquid from settled solid or immiscible liquids.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. B

A wrong: Iron remains mixed with sulfur after filtration.
B right: Magnet removes iron; water dissolves salt; filtration removes sulfur; evaporation gives salt.
C wrong: Heating iron and sulfur may cause a chemical reaction.
D wrong: Magnet cannot remove iron from filtrate after iron has already been filtered off.

27. C

A wrong: Cooling reduces kinetic energy.
B wrong: Particles become closer during condensation.
C right: Slower particles allow attractive forces to pull them closer together.
D wrong: Particles never stop moving completely unless at absolute zero.

28. B

A wrong: They are solids; boiling point is irrelevant here.
B right: Add water so the soluble solid dissolves, then filter off the insoluble solid.
C wrong: Chromatography is not suitable for bulk solid separation.
D wrong: Simple distillation separates solvent from solution.

29. A

A right: Faster spreading at higher temperature supports diffusion because particles move faster.
B wrong: Being a liquid first does not challenge the air-current idea.
C wrong: Low boiling point explains evaporation, not directly diffusion.
D wrong: Being a mixture is irrelevant.

30. B

A wrong: Melting absorbs energy.
B right: Melting is endothermic because particles overcome some attractive forces.
C wrong: Particles move faster, not slower.
D wrong: Melting is a physical change, not formation of new chemical bonds.

31. B

Dye X distance = 0.25 × 16 = 4 cm
Dye Y distance = 0.75 × 16 = 12 cm
Distance apart = 12 – 4 = 8 cm

A wrong: 4 cm is only X’s distance.
B right: 8 cm is the difference.
C wrong: 12 cm is only Y’s distance.
D wrong: 16 cm is the solvent front distance.

32. C

A wrong: Lower temperature slows particles.
B wrong: Higher Mr usually means slower diffusion.
C right: Higher temperature increases particle kinetic energy and diffusion rate.
D wrong: Diffusion is generally slower in liquids than gases.

33. B

A wrong: Chalk does not boil before water.
B right: Chalk is insoluble, so filter paper traps it.
C wrong: Chalk does not dissolve and crystallise.
D wrong: Water can evaporate.

34. C

A wrong: Fixed regular lattice describes a solid.
B wrong: Far apart particles describe a gas.
C right: Liquid particles are close together but can slide/move past each other.
D wrong: Liquids have forces of attraction.

35. A

A right: Far apart particles filling the container describe a gas.
B wrong: A gas does not have to be boiling.
C wrong: Particle spacing does not prove purity.
D wrong: Filling a container is a property of gases, not necessarily diffusion.

36. A

A right: Filter removes glass, then fractional distillation separates ethanol from water.
B wrong: Crystallisation is not used to obtain ethanol.
C wrong: Ethanol and water are miscible, so separating funnel will not work.
D wrong: Sublimation is irrelevant.

37. B

A wrong: One spot does not definitely prove purity because another solvent may separate it.
B right: Safest conclusion: only one coloured substance is shown in that solvent system.
C wrong: It clearly contains at least one coloured dissolved substance.
D wrong: Rf values can change with solvent.

38. D

A wrong: Boiling makes particles less ordered.
B wrong: Evaporation makes particles less ordered.
C wrong: Melting makes particles less ordered.
D right: Freezing forms a more ordered solid structure.

39. A

A right: Dissolve the soluble salt, filter off insoluble impurity, then crystallise the salt.
B wrong: Filtering before dissolving will not separate properly.
C wrong: Crystallisation before dissolving is nonsense chemistry.
D wrong: Filtering before crystals form removes impurity, but the sequence is badly timed and incomplete.

40. C

A wrong: Impurities usually raise boiling point or make boiling occur over a range.
B wrong: Pure liquids boil at fixed temperatures.
C right: Boiling occurs throughout the liquid when bubbles of gas form.
D wrong: Evaporation happens only at the surface; boiling happens throughout.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. D

A wrong: Hydrogen does not contain more particles just because it is lighter.
B wrong: Nitrogen does not contain more particles.
C wrong: Carbon dioxide does not contain more particles.
D right: Equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

42. A

A right: Sharp melting point suggests purity.
B wrong: Mixtures usually melt over a range.
C wrong: Melting point does not show solubility.
D wrong: Hydrated substances may lose water; not enough evidence.

43. C

A wrong: Flammable liquid should not be heated directly with a Bunsen burner.
B wrong: Filtration cannot separate dissolved solid from liquid.
C right: Distillation using an electric heater or water bath safely obtains the flammable liquid.
D wrong: Crystallisation obtains solid, not liquid.

44. B

A wrong: Gas to liquid is condensation.
B right: Sublimation is solid directly to gas.
C wrong: Liquid to gas is evaporation/boiling.
D wrong: Gas to solid is deposition, not sublimation.

45. B

A wrong: A different solvent may separate them.
B right: Solvent Q is better because the dyes travel different distances.
C wrong: Same Rf means poor separation.
D wrong: Same movement in one solvent does not prove same substance.

46. B

Methane Mr = 16, carbon dioxide Mr = 44.
A gas slower than methane but faster than carbon dioxide must have Mr between 16 and 44.

A wrong: NH3 Mr = 17, almost as fast as methane; possible mathematically, but less clearly between the two compared with oxygen.
B right: O2 Mr = 32, so it diffuses slower than methane but faster than CO2.
C wrong: SO2 Mr = 64, slower than CO2.
D wrong: H2 Mr = 2, faster than methane.

47. B

A wrong: Melting then freezing involves liquid stage.
B right: Naphthalene sublimes to gas, then deposits as solid crystals on a cooler surface.
C wrong: Condensation forms liquid, not solid crystals.
D wrong: No solution is involved.

48. B

A wrong: There are small spaces, but much less than in gases.
B right: Liquid particles are close together, so volume cannot be reduced much.
C wrong: Liquid particles are not fixed.
D wrong: Rapid straight-line motion describes ideal gas particles.

49. B

A wrong: Salt does not decompose on cooling.
B right: Cooling lowers solubility, so crystals form from a saturated solution.
C wrong: Water does not become insoluble in salt.
D wrong: Salt does not change into an element.

50. C

A wrong: Filtration uses insolubility and particle size, not boiling points.
B wrong: Crystallisation depends mainly on solubility changes, not just particle size.
C right: Fractional distillation separates substances using different boiling points.
D wrong: Chromatography depends on solubility and attraction to stationary phase, not melting points.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.