Assertion: `E^(@)` for `Mn^(3+)//Mn^(2+)` is more positive than `Cr^(3+)//Cr^(2+)`
Reason: The third ionisation energy of `Mn` is larger than that of `Cr`.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If the assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If assertion is false but reason is true.

Answer

B

Explanation

It is known that the value of `E^(@)` becomes more negative down the series. As the chromium is present below in electrochemical series than `Mn`, so `Mn` has more positive `E^(@)` value than `Cr`.
`Mn rarr 3d^(5)4s^(2)" "Mn^(2+)rarr 3d^(5)4s^(0)`
`Cr rarr 3d^(5)4s^(1),Cr^(2+) rarr 3d^(4)4s^(0)`
For elimination of one electron from `Mn^(2+)` more energy is required due to its stabel configuration . That is why third Ionisation energy of `Mn` is larger than `Cr`.