It is found that sometimes a relatively less stable oxidation state undergoes an oxidation - reduction reaction in which it is simultaneously oxidised and reduced. This is called disproportionation.

For example,

3CrO₄³⁺ + 8H⁺ → 2CrO₄^2- + Cr³⁺+ 4H₂O

Cr(V)                     Cr(VI)      Cr(III)

Cr(V) is oxidized to Cr(VI) and reduced to Cr(III).

(ii) 3MnO₄^2- + 4H⁺ → 2MnO₄^- + MnO₂ + 2H₂O

    Mn(VI)                   Mn(VII)        Mn(IV)

Mn (VI) is oxidized to Mn (VII) and reduced to Mn (IV).