For the reaction: ${\mathrm{PCl}}_5\left(g\right)\rightleftharpoons {\mathrm{PCl}}_3\left(g\right)+{\mathrm{Cl}}_2\left(g\right)$. The forward reaction at constant temperature is favoured by :

introducing ${\mathrm{PCl}}_5$ at constant volume

 increasing the volume of the container

introducing an inert gas at constant pressure

introducing chlorine gas at constant volume