Each $Mg$ atom has an oxidation number equal to $+2$, and each $N$ has an oxidation number equal to $-3$.
Work Step by Step
According to rule 6(c), $Mg$ has an oxidation number equal to $+2$. According to rule 3, the sum of the oxidation numbers must be equal to 0. Since we have $Mg_3N_2$, and we know that $Mg$ has $+2$, let's call the oxidation number for nitrogen "x": (+2) * 3 + (x) * 2 = 0 6 + 2x = 0 2x = -6 x = -3 The oxidation number of the nitrogen atoms in this compound is equal to $-3$.