Which of the following is paramagnetic?

Options

A. `[Co(NH_(3))_(6)]^(3+)`
B. `[Ni(CO)_(4)]`
C. `[Ni(NH_(3))_(4)]^(2+)`
D. `[Ni(CN)_(4)]^(2-)`

Answer

C

Explanation

`Ni(Z = 28) : [Ar]^(18)4s^(2)3d^(8)`
`Ni^(2+) : [Ar]^(18)3d^(8)`
`[Ni(NH_(3))_(4)]^(2+)` : `Ni^(2+)` undergoes `sp^(3)`-hybridisation the resulting ion is paramagnetic due to the presence two unpaired electrons .
`Ni(CO)_(4)` : Two 4s-electrons in Ni pair up with 3d-electrons followed by `sp^(3)`-hybridisation . The rasulting complex has no unpaired electron and is diamagnetic.
`[Ni(CN)_(4)]^(2-)` : `CN^(-)` being a strong ligand , pairs up the two unpairad electrons in d-subshell of `Ni^(2+)` . This is followed by `dsp^(2)`-hybridisation . The complex ion has on unpaired electron and is diamagnetic.
`[Co(NH_(3))_(6)]^(3+)` : `Co^(3+)` with `3d^(6)`-configuration undergoes `d^(2)sp^(3)`-hybridisation , after pairing up of all the six d-electrons in three d-orbitals . As the ion has no unpaired electron , it is diamagnetic.