Permanganate oxidises sulphite to sulphate in acidic solutions.

Explanation

a) The ionic skeleton equation is written as
`MnO_(4)^(-)+SO_(3)^(2-)overset(H^(+))rarrMn^(2+)+SO_(4)^(2-)`
b) Writing oxidation numbers
`overset(+7)(Mn)overset(-2)(O_(4)^(-))+overset(+4)(S)overset(-2)(O_(3)^(-2))rarroverset(+2)(Mn^(+2))+overset(+6)(S)overset(-2)(O_(4)^(-2))`
d) Dividing hte reaction into two halves and balancing in acidic medium, separately
Oxidation half - reaction : `SO_(3)^(2-)rarrSO_(4)^(2-)`
Step - 1 : Balance oxygen atoms
`SO_(3)^(2-)+H_(2)OrarrSO_(4)^(2-)`
Step - 2 : Balance hydrogen atoms in acidic medium
`SO_(3)^(2-)+H_(2)Orarr2H^(+)+SO_(4)^(2-)`
Step - 3 : Balance the charge
`SO_(3)^(2-)+H_(2)Orarr2e^(-)+2H^(+)+SO_(4)^(2-)" .....(a)"`
Reduction half - reaction : `MnO_(4)^(-)rarrMn^(2+)`
Step 1 : Balance oxygen atoms
`MnO_(4)^(-)rarrMn^(2+)+4H_(2)O`
Step 2 : Balance hydrogen atoms
`MnO_(4)^(-)+8H^(+)rarrMn^(2+)+4H_(2)O`
Step 3 : Balance charge
`MnO_(4)^(-)+8H^(+)+5e^(-)rarrMn^(2+)+4H_(2)O" ....(b))"`
e) Equalising the electron and adding the two halves.
`"eq (a)"xx5+"eq (b)"xx"2, we get,"`
`{:(5SO_(3)^(2-)+5H_(2)Orarr10e^(-)+5SO_(4)^(2-)+10H^(+)),(2MnO_(4)^(-)+16H^(+)+10e^(-)rarr2Mn^(2+)+8H_(2)O),(bar(2MnO_(4)^(-)+5SO_(3)^(2-)+6H^(+)rarr" ")),(" "2Mn^(2+)+5SO_(4)^(2-)+3H_(2)O):}`
This is balanced equation.