The correct option is
C Ni(CO)4 and
[Ni(CN)4]2− are diamagnetic and
NiCl2−4 is paramagnetic.
The concept you need to apply is simple. Figure out which ligand is strong and weak, and hence the electronic configuration of the metal in question.
Let's do this:
(i)
[Ni(CO)4] OS Ni is 0
Ni = (Z=28)
⇒3d8 4s2
CO is a strong field ligand, it causes pairing.
sp3-Hybridisation (tetrahedral)
There are no unpaired electrons, so the complex is diamagnetic.
Spin magnetic moment = zero.
(ii)
[Ni(CN4)2−, Ni2+=3d8
Cyano is a strong field ligand, it causes pairing.
dsp2-hybridisation (square planar)
There are no unpaired electrons so, the complex is diamagnetic.
Spin magnetic moment = zero.
(iii)
[NiCl4]2−, Ni2+=3d8
Chlorido is a weak field ligand, no pairing
sp3-hybridisation (tetrahedral)
There are two unpaired electrons, so the complex is paramagnetic.