Introduction of inert gas (at the same temperature) will affect the equilibrium if Pressure is constant and $\mathrm{\Delta }{\mathrm{n}}_{\mathrm{g}}\ne 0$
For constant volume, reaction quotient (Q) will remain constant.
For constant pressure, reaction quotient (Q) will remain constant when $\mathrm{\Delta }{\mathrm{n}}_{\mathrm{g}}=0$ .