COMEDK 2025 Evening Solved Paper

Concept:The oxidation number of an element is the charge it would have if all bonds were ionic. For alkali metals like potassium, the oxidation number is always $+1$ in all its compounds, including oxides, peroxides and superoxides.Explanation:In $\mathrm{K}_2\mathrm{O}$ (normal oxide), oxygen has oxidation number $-2$. Let $x$ be the oxidation number of $\mathrm{K}$. Then $2x + (-2) = 0 \implies 2x = 2 \implies x = +1$. In $\mathrm{K}_2\mathrm{O}_2$ (peroxide), oxygen has oxidation number $-1$ (peroxide ion $\mathrm{O}_2^{2-}$). So $2x + 2(-1) = 0 \implies 2x - 2 = 0 \implies x = +1$. In $\mathrm{KO}_2$ (superoxide), the superoxide ion $\mathrm{O}_2^-$ has a net charge of $-1$, so the total oxidation number of oxygen is $-1$. Thus $x + (-1) = 0 \implies x = +1$. In all three compounds, potassium exhibits the same oxidation state of $+1$.Answer:Option C: $+1, +1, +1$