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Reagent (X) is an important laboratory oxidant obtained from its ore pyrolusite. Fusing the ore with alkali in the presence of O2 gives a green compound (Y), which is converted to (X) by electrolysis or by ozone. On a small scale (X) is also made by disproportionation of (Y) in acidic medium. What are the products when (Y) disproportionates in a slightly alkaline (faintly basic) solution?

1. KMnO4 and Mn(2+)
2. KMnO4 and MnO2
3. MnO2 and Mn(2+)
4. K2MnO4 and Mn(2+)

Correct answer: KMnO4 and MnO2

Solution

Manganate (Mn +6) disproportionates in neutral or faintly alkaline solution to permanganate (KMnO4, +7) and manganese dioxide (MnO2, +4).

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