Correct Answer - A
The balanced chemical reaction is :
`2MnO_(4)^(-) + 5SO_(3)^(2-) + 6H^(+) rarr 2Mn^(2+) + 5SO_(4)^(2-) + 3H_(2)O`
`because` 5 moles `SO_(3)^(2-)` reacts with 2 moles of `KMnO_(4)`
`:.` 1 mole of `SO_(3)^(2-)` will reacts with `(2)/(5)` mole `KMnO_(4)`.