JEE Advanced · 2020 · 27 Sep 2020 · Paper 1 · s-Block Elements

Among the given compounds, only $\mathrm{KO}{}_2$ (potassium superoxide) liberates $\mathrm{O}{}_2$ upon hydrolysis:

$2\mathrm{KO}{}_2+2\mathrm{H}{}_2\mathrm{O}\to 2\mathrm{KOH}+\mathrm{H}{}_2\mathrm{O}{}_2+\mathrm{O}{}_2(\mathrm{g})\uparrow$

The other compounds either do not react with water ($\mathrm{Pb}{}_3\mathrm{O}{}_4$) or produce only $\mathrm{H}{}_2\mathrm{O}{}_2$ without liberating $\mathrm{O}{}_2$ ($\mathrm{Na}{}_2\mathrm{O}{}_2$ and $\mathrm{Li}{}_2\mathrm{O}{}_2$).