The magnitude of magnetic moment (spin only ) of `[NiCl_(4)]^(2-)` will be

Explanation

`[NiCI_(4)]^(2-)`
The oxidation number of Ni is + 2 Atomic number `=28`
`Ni =[Ar]3d^(8) 4s^(2)`
`Ni^(2+) =[Ar]3d^(8)`
Chlorido is a weak filed ligand no pairing `sp^(3)` hybridisation (tetrahedral) There are two unpaired electrons, so the complex is paramagnetic Spin magnetic moment
`mu =sqrt((n+2)) = sqrt(2(2 +2)) =sqrt8 BM`
`[Ni (CN)_(4)]^(2-)`
The oxidation number of Ni is +2
Atomic number `=28`
`Ni =[Ar] 3d^(8) 4s^(2)`
`Ni^(2+) =[Ar]3d^(8)`
Cyano is a strong filed lignad it causes pairing
`dsp^(2)` hybridisation (Square planar) There are no unpaired electrons so the complex is diamagnetic Spin magnetic moment is zero