Question

Calculate the oxidation number of Au in H[AuCl₄].

Answer 1

H⁺ (outside the brackets) → charge = +1

Inside the brackets: [AuCl₄]^– → overall charge = –1

Let oxidation number of Au = x

Each Cl = –1

Total for 4 Cl = –4

x – 4 = –1

x = +3

∴ The oxidation number of Au in H[AuCl₄] is +3.