`MnO_(4)^(2-)` (`1` mole) in neutral aqueous medium is disproportionate to

Options

A. 2/3 mole of `MnO_(4)^(-)` and 1/3 mole of `MnO_(2)`
B. 1/3 mole of `MnO_(4)^(2-)` and 2/3 mole of `MnO_(2)`
C. 1/3 mole of `Mn_(2)O_(7)` and 1/3 mole of `MnO_(2)`
D. 2/3 mole of `Mn_(2)O_(7)` and 1/3 mole of `MnO_(2)`

Answer

A

Explanation

`overset(+6)(MnO_(4)^(2-))rarr overset(+7)(MnO_(4)^(-))+overset(+4)(MnO_(2))`
`MnO_(4)^(2-)rarrMnO_(4)^(-)+e^(-)`
`MnO_(4)^(-2)+e^(-2)+2H_(2)OrarrMnO_(2)+4OH^(-)`
Adding
`MnO_(4)^(2-)+2MnO_(4)^(-)+2H_(2)Orarr2MnO_(4)^(-)+2MnO_(2)+4OH^(-)`
`3MnO_(4)^(2-)+2H_(2)O+2MnO_(4)^(-+)MnO_(2)+4OH^(-)`
Thus 1 mole of `MnO_(4)^(2-)` disproportionates in neutral aqueous medium to 2/3 moles of `MnO_(4)^(-)` and 1/3 mole of `MnO_(2)`.