Question

At a temperature below critical temperature, nitrogen cannot be liquified on
compression.
(a) True
(b) False

Answer 1

Whenever the intermolecular forces of attraction in a gas increase to a level that molecules bind together, then liquefaction of gas takes place. Thus, a gas can be liquified either by cooling of applying appreciable pressure by the combined effect of both.

Complete Step by step answer:
Here in question, it is asked whether at a temperature below critical temperature, nitrogen can be liquified or not. So, let us understand the concept behind this.

Liquid nitrogen is the liquid state of nitrogen at a very low temperature. Let us now look into critical temperature, ${T_c}$. It is a particular temperature of gas above which the gas cannot be liquified however, high pressure is applied on the gas. i.e., Whenever the temperature is below its critical temperature, we can say that the gas can be liquefied by applying high pressure on the gas.

In our statement nitrogen is liquified by compression i.e., applying high pressure on to nitrogen gas. It states it cannot liquify below its critical temperature, which is a false statement. The correct statement is we cannot liquefy nitrogen on compression when the temperature is above its critical temperature.
Hence we can say that the given statement is false

Hence the option (b) is correct.

Note: When a gas can be liquefied by applying pressure below the critical temperature the gas is called vapour of the substance, i.e., gases below their critical temperature are called vapours. Above critical temperature and under very high-pressure gases are known as supercritical fluids. These fluids are used for speedy separation of a mixture into its component.