Correct Answer - When a particular oxidation state become less stable relative to other oxidation state , one lower, one higher. It is said to undergo disproportionation,e.g., `3Mn^(VI)O_(4)^(2-)+4H^(+) to 2Mn^(VII)O_(4)^(-)+Mn^(IV)O_(2)+2H_(2)O` `Mn(VI)` is unstable relative to `Mn(VII)` and `Mn(Iv)`.