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Acidified KMnO4 (a purple oxidising agent) is decolourised by which of the following because it acts as a reducing agent?

1. SO2
2. H2O2
3. FeSO4
4. Fe2(SO4)3

Correct answer: Fe2(SO4)3

Solution

SO2, H2O2 and FeSO4 (Fe2+) all reduce MnO4- and decolourise it; Fe2(SO4)3 contains Fe3+ which is already oxidised and cannot reduce KMnO4, so it does NOT decolourise it (the odd one out).

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