📘 CBSE Class 9 Science – Matter in Our Surroundings

📝 Part 3: MCQs (Q51–Q75)

Q51. What happens to the boiling point of a liquid when atmospheric pressure decreases?

A) Increases
B) Decreases
C) Remains same
D) Becomes zero

✅ Answer: B) Decreases

• A) Incorrect: Boiling point does not increase.
• B) Correct: Lower pressure → liquid boils at lower temperature.
• C) Incorrect: Boiling point changes with pressure.
• D) Incorrect: Never becomes zero.

Q52. Which of the following has maximum intermolecular spaces?

A) Ice
B) Water
C) Steam
D) All equal

✅ Answer: C) Steam

• A) Incorrect: Ice has least intermolecular space.
• B) Incorrect: Water has more than solids but less than gases.
• C) Correct: Steam = gas form → maximum intermolecular space.
• D) Incorrect: Not equal.

Q53. What is the physical state of matter at absolute zero?

A) Solid
B) Gas
C) Plasma
D) Motionless particles

✅ Answer: D) Motionless particles

• A) Incorrect: Not necessarily solid.
• B) Incorrect: Not gas.
• C) Incorrect: Not plasma.
• D) Correct: At 0 K, particle motion ceases → no kinetic energy.

Q54. Evaporation causes cooling because:

A) Heat is absorbed from surroundings
B) Heat is released into surroundings
C) Temperature increases
D) Kinetic energy decreases

✅ Answer: A) Heat is absorbed from surroundings

• A) Correct: Evaporation uses heat energy from surroundings → cooling.
• B) Incorrect: Heat is not released.
• C) Incorrect: Temperature falls, not rises.
• D) Incorrect: Kinetic energy increases for escaping molecules.

Q55. Which of the following substances is most compressible?

A) Oxygen
B) Water
C) Iron
D) Wood

✅ Answer: A) Oxygen

• A) Correct: Gases like oxygen are highly compressible.
• B) Incorrect: Water is liquid → slight compressibility.
• C) Incorrect: Solids like iron are incompressible.
• D) Incorrect: Wood is also incompressible.

Q56. The conversion of vapour into liquid is called:

A) Evaporation
B) Condensation
C) Fusion
D) Sublimation

✅ Answer: B) Condensation

• A) Incorrect: Evaporation = liquid → vapour.
• B) Correct: Condensation = vapour → liquid.
• C) Incorrect: Fusion = solid → liquid.
• D) Incorrect: Sublimation = solid → gas.

Q57. Which property of liquids makes cooling by sweating possible?

A) Condensation
B) Evaporation
C) Fusion
D) Sublimation

✅ Answer: B) Evaporation

• A) Incorrect: Condensation releases heat, not cooling.
• B) Correct: Evaporation of sweat absorbs body heat → cooling.
• C) Incorrect: Fusion = solid → liquid.
• D) Incorrect: Sublimation is unrelated.

Q58. Which one is not a factor affecting evaporation?

A) Humidity
B) Wind speed
C) Surface area
D) Density of liquid

✅ Answer: D) Density of liquid

• A) Incorrect: Higher humidity → slower evaporation.
• B) Incorrect: Faster wind → faster evaporation.
• C) Incorrect: Larger surface → faster evaporation.
• D) Correct: Density doesn’t directly affect rate.

Q59. Which of the following processes releases energy?

A) Evaporation
B) Sublimation
C) Condensation
D) Melting

✅ Answer: C) Condensation

• A) Incorrect: Evaporation absorbs energy.
• B) Incorrect: Sublimation absorbs energy.
• C) Correct: Condensation releases latent heat.
• D) Incorrect: Melting absorbs energy.

Q60. Which one is a mixture?

A) Sodium chloride
B) Sugar
C) Air
D) Water

✅ Answer: C) Air

• A) Incorrect: Sodium chloride is a compound.
• B) Incorrect: Sugar = compound.
• C) Correct: Air is a mixture of gases.
• D) Incorrect: Water is a compound.

Q61. What is the SI unit of pressure?

A) Torr
B) Bar
C) Pascal
D) Atmosphere

✅ Answer: C) Pascal

• A) Incorrect: Torr is non-SI.
• B) Incorrect: Bar is non-SI.
• C) Correct: Pascal (N/m²) is SI unit.
• D) Incorrect: Atmosphere is non-SI.

Q62. Which state of matter has no fixed volume or shape?

A) Solid
B) Liquid
C) Gas
D) Plasma

✅ Answer: C) Gas

• A) Incorrect: Solids have fixed shape/volume.
• B) Incorrect: Liquids have fixed volume, not shape.
• C) Correct: Gases have neither fixed shape nor volume.
• D) Incorrect: Plasma is similar to gases but charged.

Q63. Which process explains conversion of water vapour into snow at high altitude?

A) Condensation
B) Freezing
C) Sublimation
D) Deposition

✅ Answer: D) Deposition

• A) Incorrect: Condensation = vapour → liquid.
• B) Incorrect: Freezing = liquid → solid.
• C) Incorrect: Sublimation = solid → gas.
• D) Correct: Deposition = gas → solid directly.

Q64. Which state of matter is used in fluorescent lamps?

A) Solid
B) Liquid
C) Plasma
D) Gas

✅ Answer: C) Plasma

• A) Incorrect: Not solid.
• B) Incorrect: Not liquid.
• C) Correct: Fluorescent lamps contain plasma of ionized gases.
• D) Incorrect: Not ordinary gas.

Q65. Which of the following has least kinetic energy?

A) Ice
B) Water
C) Steam
D) Plasma

✅ Answer: A) Ice

• A) Correct: Solids have least kinetic energy.
• B) Incorrect: Liquids more than solids.
• C) Incorrect: Gases much higher.
• D) Incorrect: Plasma = highest.

Q66. At which condition can a gas be liquefied?

A) Low pressure, low temperature
B) High pressure, low temperature
C) High pressure, high temperature
D) Low pressure, high temperature

✅ Answer: B) High pressure, low temperature

• A) Incorrect: Low pressure resists liquefaction.
• B) Correct: Cooling + compressing → liquefies gases.
• C) Incorrect: High temp prevents liquefaction.
• D) Incorrect: Same reason.

Q67. Which of the following has highest diffusion rate?

A) Oxygen
B) Ammonia
C) Carbon dioxide
D) Nitrogen

✅ Answer: B) Ammonia

• A) Incorrect: Oxygen heavier than ammonia.
• B) Correct: Light molecules diffuse faster → ammonia.
• C) Incorrect: CO₂ is heavier.
• D) Incorrect: Nitrogen diffuses slower than ammonia.

Q68. Which of the following is an example of deposition?

A) Snow formation from water vapour
B) Ice melting into water
C) Boiling of water
D) Evaporation of alcohol

✅ Answer: A) Snow formation from water vapour

• A) Correct: Vapour → solid directly.
• B) Incorrect: Melting is solid → liquid.
• C) Incorrect: Boiling = liquid → vapour.
• D) Incorrect: Evaporation = liquid → vapour.

Q69. Which of the following has definite volume but indefinite shape?

A) Solid
B) Liquid
C) Gas
D) Plasma

✅ Answer: B) Liquid

• A) Incorrect: Solid has fixed shape & volume.
• B) Correct: Liquids have volume, take container’s shape.
• C) Incorrect: Gases have neither.
• D) Incorrect: Plasma = gas-like.

Q70. Which temperature is known as absolute zero?

A) 0°C
B) –100°C
C) –273°C
D) –373°C

✅ Answer: C) –273°C

• A) Incorrect: Freezing point of water.
• B) Incorrect: Not absolute zero.
• C) Correct: Absolute zero = 0 K = –273°C.
• D) Incorrect: Too low.

Q71. Which of the following processes occurs in a pressure cooker?

A) Decrease in boiling point
B) Increase in boiling point
C) No effect on boiling point
D) Water evaporates at same temperature

✅ Answer: B) Increase in boiling point

• A) Incorrect: Pressure increases boiling point.
• B) Correct: Higher pressure → water boils above 100°C.
• C) Incorrect: Boiling point is affected.
• D) Incorrect: Temperature rises higher.

Q72. The temperature at which a liquid changes to vapour is called:

A) Freezing point
B) Melting point
C) Boiling point
D) Condensation point

✅ Answer: C) Boiling point

• A) Incorrect: Freezing = liquid → solid.
• B) Incorrect: Melting = solid → liquid.
• C) Correct: Boiling = liquid → vapour at fixed temp.
• D) Incorrect: Condensation = vapour → liquid.

Q73. Which is NOT true about solids?

A) They have fixed shape
B) They are incompressible
C) They have high intermolecular forces
D) They diffuse rapidly

✅ Answer: D) They diffuse rapidly

• A) Incorrect: True.
• B) Incorrect: True.
• C) Incorrect: True.
• D) Correct: Solids diffuse very slowly, not rapidly.

Q74. Which process explains wet clothes drying in shade?

A) Boiling
B) Evaporation
C) Condensation
D) Freezing

✅ Answer: B) Evaporation

• A) Incorrect: Boiling requires heat, not in shade.
• B) Correct: Evaporation occurs at all temperatures.
• C) Incorrect: Condensation opposite.
• D) Incorrect: Freezing not involved.

Q75. Which of these will evaporate faster?

A) Water in a glass
B) Water spread on floor
C) Water in a closed bottle
D) Ice cubes

✅ Answer: B) Water spread on floor

• A) Incorrect: Smaller surface area.
• B) Correct: Larger surface area → faster evaporation.
• C) Incorrect: Closed bottle restricts evaporation.
• D) Incorrect: Ice must melt first.

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