HOTS Questions: Particulate Nature of Matter | Science Curiosity Class 8 - New NCERT PDF Download

Q1: The temperature at which a liquid starts boiling at atmospheric pressure is known as – 
(a) Melting point
(b) Boiling point
(c) Latent heat
(d) Condensation
Ans: (b)

​When a liquid is heated, it eventually reaches a temperature at which the vapour pressure is large enough that bubbles form inside the body of the liquid. This temperature is called the boiling point.

Q2: The physical state of matter which can be easily compressed – 
(a) Liquid
(b) Gas
(c) Solid
(d) None of these
Ans: (b)

In gases, the atoms are much more spread out than in solids or liquids, and the atoms collide randomly with one another. A gas will fill any container, but if the container is not sealed, the gas will escape. Gas can be compressed much more easily than a liquid or solid.

Q3: The process for the change of a solid directly into its vapour is called  
(a) Evaporation
(b) Precipitation
(c) Condensation
(d) Sublimation
Ans: (d)

Sublimation is the process through which a solid substance changes directly into a vapour or a gaseous state without passing through a liquid state. Dry ice is a common example of this process.

Q4: Camphor changes to a gaseous state without changing into a liquid. 
(a) True
(b) False
Ans: (a)

 It's true because camphor is sublime, and it changes directly into gas without passing through the state of liquid. The process in which a solid directly changes into a gas without passing through the state of liquid is called sublimation.

Q5: Evaporation is a bulk phenomenon. 
(a) True
(b) False
Ans: (b)

Evaporation is not a bulk phenomenon; it is a surface phenomenon.

• In evaporation, only the molecules at the surface of a liquid gain enough energy to escape into the air as gas.

• The entire bulk of the liquid does not participate in evaporation at once, unlike boiling, which is a bulk phenomenon where bubbles form throughout the liquid.

Q6: Intermolecular forces are maximum in solids and minimum in gases. 
(a) True
(b) False
Ans: (a)

• Intermolecular force refers to the force that exists between two or more molecules. 
• Intermolecular force of attraction is maximum in solids. 
• This is because molecules in solid remain very close to each other which allot a definite shape to the objects that are solid. 
• It is lesser in liquids and least in the gases.

Q7: Kinetic energy of molecules is directly proportional to          
(a) Temperature
(b) Pressure         
(c) Both (a) and (b)
(d) Atmospheric pressure
Ans: (a)

According to the kinetic theory of gases, the average kinetic energy of gas molecules is directly proportional to the temperature of the gas (measured in Kelvin). This means:

• If the temperature increases, molecules move faster, so their kinetic energy increases.

• If the temperature decreases, molecules move slower, so their kinetic energy decreases.