PCl₅ dissociates as ${\mathrm{PCl}}_5\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{PCl}}_3\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$

5 moles of ${\mathrm{PCl}}_5$ are placed in a 200 litre vessel which contains 2 moles of ${\mathrm{N}}_2$ and is maintained at $600 \mathrm{K}$. The equilibrium pressure is $2.46 \mathrm{atm}$. The equilibrium constant ${\mathrm{K}}_{\mathrm{p}}$ for the dissociation of ${\mathrm{PCl}}_5$ is____________ $\times {10}^{-3}$. (nearest integer)
(Given:$\mathrm{R}=0.082 \mathrm{L}$ atm ${\mathrm{K}}^{-1}{ \mathrm{mol}}^{-1}$ : Assume ideal gas behaviour)