For a very small extent of dissociation of $PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g)$ is a gaseous phase reaction then degree of dissociation, x:

Question

(a) $x \propto P$

(b) $ x \propto \frac{1}{P}$

(c) $ x \propto \sqrt{P} $

(d) $ x \propto \sqrt{\frac{1}{P}}$