Concept:The formation of a superoxide requires a very large, low-charge-density metal cation to stabilize the bulky, unstable superoxide anion (\( \text{O}_2^- \)).
Solution:- Beryllium & Magnesium: Group 2 metals with high charge density (+2 charge). They only form normal oxides (e.g., MgO).
- Lithium: Group 1, but possesses an anomalously small atomic radius and high charge density. It only forms normal oxide (\( \text{Li}_2\text{O} \)).
- Potassium (K): is a massive alkali metal located lower down in Group 1. Its large ionic radius and low +1 charge density provide the perfect electrostatic environment to stabilize the superoxide ion.
- When burned in excess oxygen, Potassium forms the bright orange Potassium superoxide (\( \text{KO}_2 \)).
Why other options are incorrect:- The cations of Be, Mg, and Li are physically too small to stabilize the large superoxide lattice, which would immediately collapse into a normal oxide.
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