Dear Student,
The answer is as follows;
a.) oxidation number for N2 = 0
oxidation state for NH3 = -3
So total 3 equivalent of electrons transferred per ammonia molecule
Equivalent weight of NH3 = MNH3/3 (where M = molecular weight)
b.) Now total number of electron transferred involved is 6 for N2 molecule (3 electrons per nitrogen)
The equivalent weight is = MN2/6 (where M = molecular weight)
Regards