Some inert gas is added at constant volume to the following reaction at equilibrium ${\mathrm{NH}}_4\mathrm{HS}\left(\mathrm{s}\right)\rightleftharpoons {\mathrm{NH}}_3\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)$

 Pr.edict the effect of adding the inert gas

the value of K_p is increased

the equilibrium remains unaffected

the equilibrium shifts in the backward direction

the equilibrium shifts in the forward direction