For the four successive transition elements (Cr, Mn, Fe, and Co), the stability of `+2` oxidation state will be there in which of the following order ?
`(At. Nos. Cr = 24, Mn = 25, Fe = 26, Co = 27)`

Options

A. `Cr gt Mn gt Co gt Fe`
B. `Mn gt Fe gt Cr gt Co`
C. `Fe gt Mn gt Co gt Cr`
D. `Co gt Mn gt Fe gt Cr`

Answer

B

Explanation

`Mn^(2+) (d^(5))` gets highest stabilization due to half-filled configuration. In case of `Fe^(2+) (d^(6))`, addition of one extra electron in the subshell destabilizes it. Addition of two electrons in case of `Co^(2+) (d^(7))`, destabilizes it more. `Cr^(2+) (d^(4))` has one vacant subshell . `Fe^(2+)` gets more stablization as compared to `Cr` through exchange energy. So correct order is `Mn gt Fe gt Cr gt Co`.