The value of vanderwaal’s constant ‘a’ for the gases O2,N2,NH3 and CH4 are 1.360, 1.390, 4.170 and 2.253 L2 atm mol−2 respectively. The gas which can most easily be liquefied is
Greater the value of ‘a’. i.e, Intermolecular forces of attraction for a gas, more easily the gas will be liquefied.