Compressibility factor for $1$ mole of a van der Waals' gas at $0^{\circ} C$ and $100$ atmospheric pressure is found to be $0.5$ the volume of gas molecules is :
Compressibility factor $(Z)=\frac{P V}{n RT}$
For ideal gas $P V=n R T$
$\therefore Z=1$
For real gas $P V \neq n R T$
$\therefore Z \neq 1$
$0.5=\frac{100 \times V}{1 \times 0.82 \times 273}$
$V=0.1119\, L$