c
As we know, $C_P-C_v=E$ where $C_p$ and $C_v$ are molar specific heat capacities
or, ${C_P} - {C_v} = \frac{R}{M}$
For hydrogen $(M = 2){C_p} - {C_v} = a = \frac{R}{2}$
$For\,nitrogen\left( {M = 28} \right){C_p} - {C_v} = b = \frac{R}{{28}}$
$\therefore \,\frac{a}{b} = 14\,\,or,\,\,a = 14b$