(A) [Ni(CN)4]2− and [NiCl4]2− are diamagnetic and Ni(CO)4 is paramagnetic.
(B) Ni(CO)4 is diamagnetic and [NiCl4]2− and [Ni(CN)4]2− are paramagnetic.
(C) Ni(CO)4 and [NiCl4]2− are diamagnetic and [Ni(CN)4]2− is paramagnetic.
(D) Ni(CO)4 and [Ni(CN)4]2− are diamagnetic and [NiCl4]2− is paramagnetic.
Correct Answer: (D)
In Ni(CO)4, nickel is in the zero oxidation state. CO is a strong field ligand and causes complete pairing of electrons, making Ni(CO)4 diamagnetic.
In [Ni(CN)4]2−, nickel is in +2 oxidation state. CN⁻ is a strong field ligand and leads to square planar geometry with all electrons paired, hence it is diamagnetic.
In [NiCl4]2−, Cl⁻ is a weak field ligand. The complex has tetrahedral geometry with unpaired electrons, therefore it is paramagnetic.
Hence, Ni(CO)4 and [Ni(CN)4]2− are diamagnetic while [NiCl4]2− is paramagnetic.
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