Correct option: C.$Ni(CO)_4$ and $[Ni(CN)_4]^{2-}$ are diamagnetic and $[NiCl_4]^{2-}$ is paramagnetic
c
$\left[ Ni ( CO )_4\right]$
The oxidation number of $Ni$ is $O$.
Atomic number $=28$
$Ni =[ Ar ] 3 d ^8 4 s ^2$
$sp ^3$-Hybridization (tetrahedral)
There are no unpaired electrons, so the complex is diamagnetic.
Spin magnetic moment = zero
$\left[ Ni ( CN )_4\right]^{2-}$
The oxidation number of $Ni$ is $+2$.
Atomic number $=28$
$Ni =[ Ar ] 3 d ^8 4 s ^2$
$Ni ^{2+}=[ Ar ] 3 d ^8$
$dsp ^2$-Hybridization (square planar)
There are no unpaired electrons so, the complex is diamagnetic.
Spin magnetic moment $=$ zero
$\left[ NiCl _4\right]^{2-}$
The oxidation number of $Ni$ is $+2$.
Atomic number $=28$
$Ni =[ Ar ] 3 d ^8 4 s ^2$
$Ni ^{2+}=[ Ar ] 3 d ^8$
Chlorido is a weak field ligand, no pairing
$sp ^3$-Hybridization (tetrahedral)
There are two unpaired electrons, so the complex is paramagnetic.
Spin magnetic moment
$\mu=\sqrt{ n ( n +2)}\,BM$
$=\sqrt{2(2+2)} BM =\sqrt{8}\,BM$
