If the bond dissociation energies of XY, X2 and Y2 (all diatomic molecules) are in the ratio of 1 : 1 : 0.5 and ΔHf for the formation of XY is –200kJ mol–1. The bond dissociation energy of X2 will be
(a) 100kJ mol–1
(b) 200kJ mol–1
(c) 800kJ mol–1
(d) 400kJ mol–1