What is meant by 'disproportionation'? Give two examples of disproportionation reaction in aqueous solution.

Explanation

When the oxidation state of an element in a reactant increases in one of the products and decreases in the other product, the phenomenon is called proportionation.
For example, Mn (VI) in `MnO_(4)^(2-)+4` changes to Mn (VII) in the product `MnO_(4)^(-)` and to Mn (IV) in the product `MnO_(2)` as shown by the reaction :
`3MnO_(4)^(2-)+4H^(+)to 2MnO_(4)^(-)+MnO_(2)+2H_(2)O`
Similarly, Cr (V) undergoes disproportionation in acidic medium as follows :
`CrO_(4)^(3-)+8H^(+)to overset(VI)(2CrO_(4)^(2-))+overset(III)(Cr^(3+))+4H_(2)O`