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 gtFe gt Cr gt Co`
C. `Fe gt Mn gt Co gt Cr`
D. `Co gt Mn gt Fegt Cr`

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 incase of `Co^(2+)(d^(7))` destabilizes itmore . `Cr^(2+)(d^(4))` has one vacant subshell. `Fe^(2+)` gets more stabilizationas compared to `Cr^(2+)` through exchange energy . So, the correct order is`Mn gt Fe gt Cr gtCo`.