The d electron congfiguration of `Cr^(2+)` , `Mn^(2+)` , `Fe^(2+)` and `Ni^(2+)` are `3d^(4)` , `3d^(5)` , `3d^(6)` and `3d^(8)` respectively. Which one of the folowing aqua complexes will exhibit the minimum paramagnetic behaviour ?
`(At. No . Cr = 24, Mn = 25, Fe = 26, Ni = 28)`

Options

A. `[Ni(H_(2)O)_(6)]^(2+)`
B. `[Cr(H_(2)O)_(6)]^(2+)`
C. `[Mn(H_(2)O)_(6)]^(2+)`
D. `[Fe(H_(2)O)_(6)]^(2+)`

Answer

A

Explanation

Since water `(H_(2)O)` is a weak field ligan, there is no resuffle of electronic configuration. Thus, d electron configuration of metal ions and complex ions is the same.
`Cr^(2+) (3d^(4))implies 4` unpaired electrons
`Mn^(2+) (3d^(5)) implies 4` unpaired electrons
`Fe^(2+) (3d^(6)) implies 4` unpaired electrons
`Ni^(2+) (3d^(8)) implies 2` unpaired electrons
Since paramagnetic behavoiur is directly proportional to the number of unpaired d electrons, `[Ni(H_(2)O)_(6)]^(2+)` will exhibit minimum paramagnetic behaviour.