Question

A gas can be liquefied by:

• A. cooling
• B. compressing
• C. Both $1$ and $2$
• D. None of these

Answer 1

The correct option is C Both $1$ and $2$

A gas can be liquefied by cooling and compressing.
During cooling, the temperature of the gas is lowered and during compression, the pressure on the gas is increased.
A gas can be liquefied by pressure, only if it is at or below its characteristic temperature called critical temperature.

Hence, the correct option is $\text{C}$