If C_P and C_V denote the specific heats of nitrogen per unit mass at constant pressure and constant volume respectively, then

Suppose specific heat per unit mole = S 
We know that ${\mathrm{S}}_{\mathrm{p}}-{\mathrm{S}}_{\mathrm{V}}=\mathrm{R}$
or   ${\mathrm{M}}_0\left({\mathrm{C}}_{\mathrm{p}}-{\mathrm{C}}_{\mathrm{V}}\right)=\mathrm{R} ...\left(1\right)$
where $\mathrm{S}={\mathrm{M}}_0\mathrm{C}$
From eq. (1), we get
$\left({\mathrm{C}}_{\mathrm{p}}-{\mathrm{C}}_{\mathrm{V}}\right)=\frac{\mathrm{R}}{{\mathrm{M}}_0}=\frac{\mathrm{R}}{28} ...\left(2\right)$
where M_o = Molar mass = 28 for nitrogen.