X2+Y2→2XY,∆H=2(−200) Let x be the bond dissociation energy of X2. Then ∆H=−400 ‌=ξx−x+ξy−y−2ξx−y ‌=x+0.5x−2x ‌=−0.5x or x=‌
400
0.5
=800‌kJ‌mol−1 (In the question paper, this option was not mentioned. So the answer has been marked ' N′ )