The stability of complexes of `Cu^(2+),Ni^(2+),Co^(2+)` and `Fe^(2+)` varies in the order

Options

A. `Cu^(2+)gtNi^(2+)gtCo^(2+)gtFe^(2+)`
B. `Cu^(2+)gtFe^(2+)gtNi^(2+)gtCo^(2+)`
C. `Ni^(2+)gtCo^(2+)gtFe^(2+)gtCu^(2+)`
D. `Cu^(2+)ltNi^(2+)ltCo^(2+)ltFe^(2+)`

Answer

D

Explanation

When cations have same charge but number of d-electrons are different then the stability (or CFSE) decreases with increases in the number of d-electrons.
Therefore, the correct order is
`"Fe"^(2+)gt"Co"^(2+)gt"Ni"^(2+)gt"Cu"^(2+)`