What are the oxidation numbers of each element in these examples: a) H2SO4 b) N2 c) NH4+

a) H₂SO₄ ANSWER: H: +1 S: +6 O: -2 b) N₂ ANSWER: N: 0 (all elements not within a compound have an oxidation number of 0 eg I₂, O₂, K) c) NH₄⁺ ANSWER: N: -3 H: +1 (sum of oxidation numbers within compound should equal the overall charge of the compound)