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Why is the E^(ϴ) value for the Mn^(3+)//...

Why is the `E^(ϴ)` value for the `Mn^(3+)//Mn^(2+)` couple much more positive than that for `Cr^(3+)//Cr^(2+)" or "Fe^(3+)//Fe^(2+)` ? Exaplain.

Text Solution

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Much larger third ionisation energy of Mn ( where the required change is `d^(5)` to `d^(4)`) is mainly responsible for this. This also explains why the +3 sate of Mn is of little importance .
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