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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: 2/5

Solution

The balanced chemical equation for the reaction between KMnO4 and sulphite ion is 2KMnO4 + 5SO3 + 3H2SO4 -> K2SO4 + 2MnSO4 + 5SO2 + 3H2O. From the equation, 2 moles of KMnO4 are required to react with 5 moles of sulphite ion. Therefore, 2/5 moles of KMnO4 are required to react with 1 mole of sulphite ion.

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