MHT CET Chemistry Question (2026) — Solution

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Alkali metals react with oxygen to form different types of oxides depending on their size. Lithium forms mainly monoxide (Li_ 2 O). Sodium forms mainly peroxide (Na_ 2 O_ 2 ). Potassium, rubidium, and cesium form mainly superoxides (MO_ 2 ) due to the stabilization of the large superoxide ion by large cations. Magnesium forms mainly monoxide (MgO). Therefore, potassium forms a superoxide with oxygen. Answer: Potassium