Phosphorus pentachloride dissociates as follows in a closed reaction vessel,

${\mathrm{PCl}}_5\left(\mathrm{g}\right) \rightleftharpoons {\mathrm{PCl}}_3\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$. If total pressure at equilibrium of the reaction mixture is $\mathrm{p}$ and degree of dissociation of ${\mathrm{PCl}}_5$ is $\mathrm{x}$, the partial pressure of ${\mathrm{PCl}}_3$ will be