${\mathrm{K}}_{\mathrm{p}}\mathrm{ }=\frac{{{\mathrm{n}}^2}_{\mathrm{N}{\mathrm{H}}_3}}{{\mathrm{n}}_{{\mathrm{N}}_2}\times {\mathrm{n}}_{{\mathrm{H}}_2}^3}\times \mathrm{ }{\left(\frac{\mathrm{P}}{\mathrm{\Sigma }\mathrm{n}}\right)}^{\mathrm{\Delta }\mathrm{n}}$

At constant pressure, with the introduction inert gas $\mathrm{\Sigma }\mathrm{n}$ increases. Since $\mathrm{\Delta }\mathrm{n}=–2$, therefore on increasing $\mathrm{\Sigma }\mathrm{n}\mathrm{ }{\left(\frac{\mathrm{P}}{\mathrm{\Sigma }\mathrm{n}}\right)}^{\mathrm{\Delta }\mathrm{n}}$ increases, but ${\mathrm{K}}_{\mathrm{p}}$ remain constant, hence no. of

moles of ${\mathrm{N}}_2\mathrm{ }\left(\mathrm{g}\right)$ & ${\mathrm{H}}_2\mathrm{ }\left(\mathrm{g}\right)$ are increased and backward reaction is favoured.