JAMB Chemistry 2014 Paper

Concept:The oxidizing agent is the substance that is reduced during a redox reaction while causing another substance to be oxidized.Explanation:In the reaction $\mathrm{H_2O}_{(g)} + \mathrm{C}_{(s)} \rightarrow \mathrm{H_2}_{(g)} + \mathrm{CO}_{(g)}$, carbon gains oxygen to form $\mathrm{CO}_{(g)}$, so carbon is oxidized.The oxidation state of carbon changes from $0$ in $\mathrm{C}_{(s)}$ to $+2$ in $\mathrm{CO}_{(g)}$.Meanwhile, the hydrogen in water changes from $+1$ in $\mathrm{H_2O}_{(g)}$ to $0$ in $\mathrm{H_2}_{(g)}$, so water is reduced.Thus, $\mathrm{H_2O}_{(g)}$ acts as the oxidizing agent: it oxidizes carbon and is itself reduced to hydrogen gas.The state symbol $(g)$ is important because the question specifies steam, not liquid water.Answer:Option C: $\mathrm{H_2O}_{(g)}$.