Discussion
The CORRECT order of stability of the given metal oxides is
Answer: B
The order is \(LiO_{2} \lt NaO_{2} \lt KO_{2} \lt RbO_{2}\).
These are superoxides, containing the large \(O_{2}^{-}\) anion. A large anion is stabilised best by a large cation, because the lattice energy gained is then favourable and the cation polarises the anion less. Going down the group, the cation grows from \(Li^{+}\) to \(Rb^{+}\), so the superoxides become steadily more stable.
That is why potassium, rubidium and caesium form superoxides directly on burning in air, while lithium forms the normal oxide \(Li_{2}O\) and sodium the peroxide. The decreasing order, and the orders that change direction part way, contradict this steady trend.
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