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The number of moles of KMnO4 that will be needed to react with one mole of sulphite ion in acidic solution is:

1. 4/5
2. 2/5
3. 1
4. 3/5

Correct answer: 4/5

Solution

In acidic medium, KMnO4 acts as an oxidizing agent and reduces MnO4⁻ to Mn²⁺. The oxidation of sulphite ion (SO₃²⁻) to sulphate ion (SO₄²⁻) involves a transfer of 2 electrons, while MnO4⁻ to Mn²⁺ involves a transfer of 5 electrons. Thus, the mole ratio of KMnO4 to SO₃²⁻ is 4:5, meaning 4/5 moles of KMnO4 are required for 1 mole of SO₃²⁻.

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