At temperature T, a compound AB2(g) dissociates according to the reaction $2{\mathrm{AB}}_2\left(\mathrm{g}\right)\rightleftharpoons 2\mathrm{AB}\left(\mathrm{g}\right)+{\mathrm{B}}_2\left(\mathrm{g}\right)$with a degree of dissociation ‘x’ which is small as compared to unity. The expression for ${\mathrm{K}}_{\mathrm{P}},$in terms of ‘x’ and total pressure ‘P’ is