$K_c = 0.04$ at $723\text{ K}$ for the following reaction:

$$PCl_{5(g)} \rightleftharpoons PCl_{3(g)} + Cl_{2(g)}\text{.}$$

The $K_p$ of the reaction will be: (where $R = 0.082\text{ atm dm}^3\text{ mol}^{-1}\text{ K}^{-1}$)