The number of moles of `KMnO_(4)` that will be needed to react with one mole of sulphite ion in acidic solution is:

Explanation

`2KMnO_(4) + 3H_(2)SO_(4) rarr K_(2)SO_(4) + 2 MnSO_(4) + 3H_(2)O + 5[O]`
`[SO_(3)^(2-) + [O] rarr SO_(4)^(2-)] xx 5 /(2KMnO_(4)^(-) + 3H_(2)SO_(4) + 5SO_(3)^(2-) rarr K_(2)SO_(4) + 2MnSO_(4) + 3H_(2)O + 5 SO_(4)^(2-))`
or `2 MnO_(4)^(-) + 6H^(+) + 5SO_(3)^(2-) rarr 2 Mn^(2+) + 5 SO_(4)^(2-) + 3H_(2)O`
Therefore, 5 moles of `SO_(3)^(2-)` will require 2 moles of `MnO_(4)^(-)`
1 mole of `SO_(3)^(2-)` will require `2/5` moles of `MnO_(4)^(-)`