Question

Assertion: A gas can be easily liquefied at any temperature below its critical temperature.
Reason: Liquefaction of a gas takes place when the average kinetic energy of the molecules is low.
a. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
b. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
c. Assertion is correct but Reason is incorrect.
d. Assertion is incorrect but Reason is correct.

Answer 1

Hint: Try to recall that critical temperature is that temperature above which it cannot be liquefied and each gas can be liquefied provided first it is cooled down to or below a particular temperature. Now, by using this you can easily answer the question.

Complete step by step solution:
1. It is known to you that the liquefaction of a gas takes place when the intermolecular forces of attraction become so high that they bind the gas molecules together to form the liquid state.
2. The intermolecular forces of attraction can be increased either by increasing the pressure so that the molecules come close together or by cooling the gas so that the kinetic energy of the molecules decreases and they become slower. Hence, a gas can be liquefied by cooling or by application of pressure or the combined effect of both.
3. The effect of temperature on the liquefaction of gases is found to be very important as higher the temperature of the gas, more difficult it is to liquefy it and higher is the pressure required.
4. For each gas, there is a particular temperature above which it cannot be liquefied howsoever high pressure may apply on the gas. This temperature is known as critical temperature.
Therefore, above we can conclude that both assertion and reason are correct but reason is not the correct explanation for assertion so option B is the correct option to the given question.

Note:
a. It should be remembered to you that the pressure required to liquefy the gas at the critical temperature is called critical pressure.
b. Also, you should remember that the volume occupied by one mole of the gas at the critical temperature and the critical pressure is called the critical volume.