JAMB Chemistry 2019 Paper

Concept:The identity of $X$ can be deduced from two tests: gas evolution with concentrated $\mathrm{H}_2\mathrm{SO}_4$ and the ability to decolorize acidified $\mathrm{KMnO}_4$.Explanation:A substance that liberates $\mathrm{CO}_2$ when treated with concentrated $\mathrm{H}_2\mathrm{SO}_4$ could be a carbonate, hydrogen carbonate, or an oxalate.However, only a reducing agent can decolorize acidified $\mathrm{KMnO}_4$.Among the options, $\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4$ (oxalic acid) is a strong reducing agent.It readily reduces purple $\mathrm{KMnO}_4$ to colourless $\mathrm{Mn}^{2+}$ ions.Also, warm concentrated $\mathrm{H}_2\mathrm{SO}_4$ decomposes oxalic acid to give $\mathrm{CO}$ and $\mathrm{CO}_2$ gases.Hence, $X$ must be oxalic acid, $\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4$.Answer:D. $\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4$