In a 500 ml flask, the degree of dissociation of $PCl_5$ at equilibrium is $40 \%$ and the initial amount is 5 moles. The value of equilibrium constant in $mol.lit^{-1}$ for the decomposition of $PCl_5$ is

Question

$$\begin {array} {1 1} (1)\;2.33 & \quad (2)\;2.66 \\ (3)\;5.32 & \quad (4)\;4.66 \end {array}$$