The correct order of normal boiling points of O₂, ${\mathrm{N}}_2,{\mathrm{NH}}_3\text{ and }{\mathrm{CH}}_4$ for whom the values of van der Waals constant ' a ' are 1.360, 1.390, 4.170 and $2.253{\mathrm{L}}^2\mathrm{atm}{\mathrm{mol}}^{-2}$ respectively is

The correct order of normal boiling points of O₂​,N₂​,NH₃​ and CH₄​ ( for whom the values of vander waals constant 'a' are 1.360, 1.390,  4.170 and 2.253 L² atm. mol⁻² respectively) is O₂​<N₂​<CH₄​<NH₃​.
Higher is the value of van der waals constant a, higher will be the boiling point as a is an indirect measure of the magnitude of attractive forces between the molecules.