`MnO_(4)^(2-)`undergoes disproportionation reaction in acidic medium but `MnO_(4)^(-)`does not .Give reason.

Explanation

The oxidation number of Mn in `MnO_(4)^(-)` is +7 , which is the highest oxidation that Mn can possess .So does not undergoes disproportionation reaction
Again is case of `MnO_(4)^(2-)` , the oxidation number of Mn is +6 . Therefore ,Mn is `MnO_(4)^(2-)` can increase its oxidation undergoes disproportionation reaction as given below
In the given above reactio the oxidation number of Mn increases from +6 in `Mn_(4)^(2-)` to +7 in `MnO_(4-)^(-)`and decreases to +4 in `MnO_(2-)`