Which from following elements form superoxide with air?

Step-by-step solution

The reaction of alkali metals with oxygen depends significantly on atomic size, as this influences the stability of the resulting oxide compounds. Lithium forms the oxide 4Li(s) + O₂ (g) 2Li₂ O(s) , while sodium yields the peroxide 2Na(s) + O₂ (g) Na₂ O₂ (s) . Larger alkali metals—potassium, rubidium, and cesium—form superoxides such as K(s) + O₂ (g) KO₂ (s) , since their size stabilizes the superoxide ion O2⁻ . Magnesium, an alkaline earth metal, reacts as 2Mg(s) + O₂ (g) 2MgO(s) . Only potassium forms a superoxid