Permanganate oxidises sulphite to sulphate in acidic solutions.

Explanation

(a) The ionic skeleton equation is written as
`MnO_(4)^(-)+SO_(3)^(2-) overset(H^(+))to Mn(2+)+SO_(4)^(2-)`
(b) Writing oxidation numbers
`overset(+7)(Mn) overset(-2)(O_(4)^(-)) +overset(+4)(S) overset(-2)(O_(3)^(-2)) to overset(+2)(Mn^(+2))+overset(+6)(S) overset(-2)(O_(4)^(-2))`
(c) Locating atoms undergoing change in oxidation numbers
`overset(+7)(Mn) O_(4)^(-) to overset(+2)(Mn^(+2)) +overset(+6)(S) O_(4)^(-2)`
(d) Dividing the reaction into two halves and balancing in acidic medium, separately.
(e) Equalising the electrons and addint the two halves.
`eq (a) xx 5 +eq (b) xx 2`, we get
`5SO_(3)^(2-)+5H_(2)O to 10e^(-)+5SO_(4)^(2-)+10H^(+)`
`2MnO_(4)^(-)+16H^(+)+10e^(-) to 2Mn^(2+)+8H_(2)O`
`=2MnO_(4)^(-)+5SO_(3)^(2-)+6H^(+) to 2Mn^(2+) +5SO_(4)^(2-)+3H_(2)O`
This is the balanced equation.