The green paramagnetic species formed by heating KMnO₄ at 513 K is:
- A.K₂MnO₄✓
- B.Mn₃O₄
- C.MnO
- D.KO₂
Correct Answer
(A) K₂MnO₄
Solution & Explanation
Concept: KMnO₄ (Mn in +7, colourless d⁰ on Mn, deep purple) is thermally unstable; on heating it disproportionates. Reaction on heating at 513 K: 2KMnO₄ →(Δ, 513 K) K₂MnO₄ + MnO₂ + O₂ The product asked for is the GREEN, PARAMAGNETIC species: • K₂MnO₄ (potassium manganate) has Mn in the +6 state. Its electronic configuration is 3d¹, i.e. ONE unpaired electron → paramagnetic, and the manganate ion MnO₄²⁻ is green. ✓ • MnO₂ (Mn +4) is a brown/black solid, and O₂ is a gas — neither is the green species. • Mn₃O₄, MnO and KO₂ are not formed in this decomposition. So the green paramagnetic species is K₂MnO₄ → answer A. Note the colour/oxidation-state link: MnO₄⁻ (+7) purple, MnO₄²⁻ (+6) green.
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