The standard enthalpy of formation of NH3 is -46.0 kJ mol-1. If the enthalpy of formation of H2 from its atoms is -436 kJ mol-1 and that of N2 is -712kJ mol-1, the average bond enthalpy of N-H bond in NH3 is
(a) -964kJ mol-1 (b) +352kJmol-1
(c) +1056 kJ mol-1 (d) -1102 kJ mol-1
