If Z is a compressibility factor, van der Waals equation at low pressure can be written as:

For gaseous state, if most probable speed is denoted by C*, average speed by $$\mathop C\limits^{\_\_} $$ and mean square speed by C, then for a large number of molecules the ratios of these speeds are:

The compressibility factor for a real gas at high pressure is :

'a’ and `b’ are van der Waals’ constants for gases. Chlorine is more easily liquefied than ethane because