2 mole of PCl5 is heated in a one litre vessel. If PCl5 dissociates to the extent of 80%, the equilibrium constant for the dissociation of PCl5 is

Vvessel = 1Degree of decomposition, α = For every 1 mole of PCl5 taken 0.8 moles decomposes.For every 2 mole of PCl5 taken 1.6 moles decomposes.1 mole of PCl5 decomposes to give 1 mole of PCl3 and 1 mole of Cl21.6 mole of PCl5 decomposes to give 1.6 mole of PCl3 and 1.6 mole of Cl2