The complex showing a spin-only magnetic moment of 2.82 B.M. is: Ni(CO)4, Ni(PPh3)4, [NiCl4]2−, [Ni(CN)4]2−

[NiCl4]2−, O.S. of Ni = +2
Ni(28) = [Ar]3d84s2
Ni2+ = [Ar]3d8
Now, Magnetic moment μ = √n(n+2) ⇒ n = Number of unpaired electrons = 2
Therefore μ = √2(2+2) = 2.82 BM
Hence, option B is correct.