WBJEE 2026 Physics and Chemistry Paper

Concept:Peroxide ion $\mathrm{O}_2^{2-}$ has all electrons paired in its molecular orbitals, so it is diamagnetic.Explanation:The molecular orbital configuration of $\mathrm{O}_2^{2-}$ contains no unpaired electrons.All electrons are paired in bonding and antibonding molecular orbitals.Substances with unpaired electrons show paramagnetism or ferromagnetism.Since $\mathrm{O}_2^{2-}$ has no unpaired electrons, it does not show such behaviour.Hence, peroxide ion is diamagnetic.Answer:C. Diamagnetic