Atomic numbers of `Cr` and `Fe` are respectively `24` and `26`. Which of the following is paramagnetic with the spin of the electron?

Options

A. `[Cr(CO)_(6)]`
B. `[Fe(CO)_(5)]`
C. `[Fe(CN)_(6)]^(4-)`
D. `[Cr(NH_(3))_(6)]^(3+)`

Answer

D

Explanation

`[Cr(CO)_(6)] implies Cr^(0) (3d^(5) 4s^(2))`
Since CO is a strong field ligand, there is resuffle of electron configuration resulting in zero unpaired electrons.
`[Fe(CO)_(5)] implies Fe^(0)(3d^(6) 4s^(2))`
Since CO is a strong field ligand, there is resuffle electron configuration resulting in zero inpaired electron resulting in zero unpaired electrons.
`[Fe(CN)_(6)]^(4-) implies Fe^(2+) (3d^(6))`
Since `CN^(-)` is a strong field ligand, there is resulffle of electron configurration resulting in zero unpaired electrons
`[Cr(NH_(3))_(6)]^(3+) implies Cr^(3+) (3d^(3))`
Than is no resutfle of electron configuration as enough d orbitals are vacant for `d^(2) sp^(3)` hybridization. Thus, there arer 3 unpaired electrons.