A quantity of ${\mathrm{P}\mathrm{C}\mathrm{l}}_5$ was heated in a $2\mathrm{ }\mathrm{l}\mathrm{i}\mathrm{t}\mathrm{r}\mathrm{e}$ vessel at $525\mathrm{ }\mathrm{K}.$ It dissociates as

${\mathrm{P}\mathrm{C}\mathrm{l}}_5\left(\mathrm{g}\right)\mathrm{ }\rightleftharpoons \mathrm{ }{\mathrm{P}\mathrm{C}\mathrm{l}}_3\left(\mathrm{g}\right)\mathrm{ }+\mathrm{ }{\mathrm{C}\mathrm{l}}_2\left(\mathrm{g}\right)$

At equilibrium $0.2\mathrm{ }\mathrm{m}\mathrm{o}\mathrm{l}$ each of ${\mathrm{P}\mathrm{C}\mathrm{l}}_5,\mathrm{ }{\mathrm{P}\mathrm{C}\mathrm{l}}_3$ and ${\mathrm{C}\mathrm{l}}_2$ is found in the reaction mixture. The equilibrium constant ${\mathrm{K}}_{\mathrm{c}}$ for the reaction is -