The reaction with KMnO4 and sulphite is as follows : MnO4−+5SO32−+6H+⟶2Mn2++5SO42−+3H2O So, one mole of sulphite (SO32−) is needed to react with
2
5
mole of MnO4−according to given reaction. Note 2 moles of MnO4− react with 5 moles of sulphite in acidic medium.