The bond dissociation enthalpies of H₂ (g), Cl₂ (g) and HCl (g) are 435, 243 and 431 kJ mol-¹ respectively. The enthalpy of formation of
HCl (g) will be

A. 247 kJ mol⁻¹
B. 770 kJ mol⁻¹
C. 1109 kJ mol⁻¹
D. -92 kJ mol⁻¹