Which of the following reactions correctly represents the formation of the superoxide ion when an alkali metal reacts with excess oxygen?

Solution

1. Lithium forms only the oxide ${\text{Li}}_2\text{O}$ with oxygen.
2. Sodium forms the peroxide ${\text{Na}}_2{\text{O}}_2$ as the major product with excess oxygen.
3. Potassium, rubidium, and cesium form superoxides ${\text{MO}}_2$ because the large cation stabilizes the large ${\text{O}}_2^{-}$ anion.
4. Hence the answer is (C).