Question

A gas can be liquefied by:
(A) cooling
(B) compressing
(C) both A and B
(D) None of these

Answer 1

Hint: Think about what liquefaction of a gas is. In our homes, we make use of LPG that is, liquid petroleum gas and nowadays, autos run on CNG that is, compressed natural gas. Both LPG and CNG are in metal cylinders. Think about how gas is filled inside these containers and then choose the suitable option.

Complete step by step answer:
- Liquefaction of gas is the process in which gas molecules are brought closer and closer to form a loose packed structure as that of liquids and gas is converted in the liquid phase.
- Liquefaction of gas is basically the process of compression of gas.
- In order to compress gas, temperature needs to be reduced so that gaseous molecules are held closer together to form liquid.
- This compression process is similar to an ice formation process like the temperature is reduced to zero degree celsius, liquid water freezes to solid ice.
- Similarly, when the temperature of gas is reduced beyond its boiling point, it gets converted into liquid form.
- In order to achieve this, pressure is kept high for compression and temperature is reduced to boiling temperature, so there is cooling effect.
- Therefore, a gas can be liquefied by compressing and cooling.
So, the correct answer is “Option C”.

Note: Remember to convert a loosely packed phase like liquid or gas into a tightly packed phase like solid or liquid, temperature needs to be reduced and pressure needs to be applied to achieve compression. For such questions, think about phase conversion of water to easily crack the question.