The variation of the compressibility factor$\left(\mathrm{Z}\right)$with pressure $(\mathrm{P} \mathrm{in} \mathrm{bar})$ for some gases, are shown in the figure below. Identify the gases $\left(\mathrm{A}\right),\left(\mathrm{B}\right)$ and $\left(\mathrm{C}\right)$.

In the nature, no gas is found to be an ideal gas under all conditions of temperature and pressure. Therefore, the gases existing in nature are called as real gases.

For an ideal gas,

$\frac{{\mathrm{PV}}_{\mathrm{m}}}{\mathrm{RT}}=\mathrm{Z}$

Here, $\mathrm{Z}$ is the compressibility factor.

$\mathrm{Z}=1$(for ideal gases)

The extent of deviation shown by real gases from ideal behaviour is expressed in terms of the compressibility factor.

Easily liquefiable gases such as ${\mathrm{CO}}_2$ exhibit larger deviation when compared to gases such as ${\mathrm{H}}_2,{\mathrm{O}}_2,\mathrm{etc}$., that liquify with difficulty.