Which of the following represents the $Van \ der \ Waals$ equation for $n$ moles of a real gas?

In Van der Waals equation of state for a non-ideal gas,the term that accounts for intermolecular forces is

The volume of gas $A$ is twice that of gas $B$. The compressibility factor of gas $A$ is thrice that of gas $B$ at the same temperature. The ratio of the pressures of the gases for equal number of moles is:

Pressure versus volume graph for a real gas and an ideal gas are shown in the figure. Answer the following questions on the basis of this graph:
$(i)$ Interpret the behaviour of real gas with respect to ideal gas at low pressure.
$(ii)$ Interpret the behaviour of real gas with respect to ideal gas at high pressure.
$(iii)$ Mark the pressure and volume by drawing a line at the point where real gas behaves as an ideal gas.

Consider the following gases and their corresponding $ 'a'$ values given in parentheses: $CH_4 (2.25), N_2 (1.35), O_2 (1.36)$,and $CO (1.46)$. Which of these gases will be the most difficult to liquefy?

Arrange the following gases in increasing order of van der Waals constant '$a$':
$A$. $Ar$; $B$. $CH_4$; $C$. $H_2O$; $D$. $C_6H_6$
Choose the correct option from the following: