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

(N/A) disproportionation reaction is a special type of redox reaction in which a species in a particular oxidation state is simultaneously oxidized and reduced.
Examples in aqueous solution:
$(i)$ $3CrO_4^{3-} + 8H^{+} \to 2CrO_4^{2-} + Cr^{3+} + 4H_2O$
Here,$Cr(V)$ is oxidized to $Cr(VI)$ and reduced to $Cr(III)$.
$(ii)$ $3MnO_4^{2-} + 4H^{+} \to 2MnO_4^{-} + MnO_2 + 2H_2O$
Here,$Mn(VI)$ is oxidized to $Mn(VII)$ and reduced to $Mn(IV)$.