JAMB Chemistry 2024 Paper

Concept:The oxidation number of an element in its free state is zero; in a compound, the sum of oxidation numbers equals zero.Explanation:In $\mathrm{H_2S}$, hydrogen has an oxidation state of $+1$ each.Let the oxidation state of sulfur be $x$.$(+1 \times 2) + x = 0$, so $x = -2$.Therefore, sulfur is in the $-2$ oxidation state in the reactant.On the product side, sulfur appears as $\mathrm{S_{(s)}}$, a free element.The oxidation state of any free element is $0$.So sulfur changes from $-2$ to $0$.Answer:The change is from $-2$ to $0$, which matches option C.