Phosphorus pentacloride dissociates as follows, in a closed reaction vessel, <br> $PCl_5 (g) \rightleftharpoons PCl_3 (g) + Cl_2(g) $ <br> If total pressure at equilibrium of the reaction mixture is $P$ and degree of dissociation of $PCl_5$ is $x$, the partial pressure of $PCl_3$ will be :
