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Fusing MnO2 with KOH in the presence of O2 gives a salt W. Electrolytic oxidation of an alkaline solution of W produces another salt X. Let the manganese-containing ions in W and X be Y and Z respectively. Which of the following statements is/are correct?

1. Y is diamagnetic whereas Z is paramagnetic
2. Both Y and Z are coloured and tetrahedral in shape
3. In both Y and Z, pi-bonding occurs between the p-orbitals of oxygen and the d-orbitals of manganese
4. In aqueous acidic solution Y disproportionates to give Z and MnO2

Correct answer: In aqueous acidic solution Y disproportionates to give Z and MnO2

Solution

W is K2MnO4 (Y = MnO4²-, green, paramagnetic, Mn +6) and X is KMnO4 (Z = MnO4⁻, purple, diamagnetic, Mn +7); in acid Y disproportionates: 3 MnO4²- + 4 H+ -> 2 MnO4⁻ + MnO2 + 2 H2O.

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