Chemistry - Coordination Chemistry Question with Solution | TestHub

The solution needs to evaluate each complex based on crystal field theory or valence bond theory.

(i) $[NiC{l}_4{]}^{2-}$: Ni²⁺ is $d^8$. Cl⁻ is a weak field ligand. $s{p}^3$, tetrahedral, paramagnetic (2 unpaired electrons). Correct.

(ii) $[Ni(N{H}_3{)}_6{]}^{2+}$: Ni²⁺ is $d^8$. NH₃ is a strong field ligand. $s{p}^3{d}^2$, octahedral, paramagnetic (2 unpaired electrons). Correct.

(iii) $[Ni(CO{)}_4]$: Ni is in 0 oxidation state, $d^{10}$. CO is a strong field ligand. $s{p}^3$, tetrahedral, diamagnetic (all electrons paired). Statement says paramagnetic, so incorrect.

(iv) $[Ni(CN{)}_4{]}^{2-}$: Ni²⁺ is $d^8$. CN⁻ is a strong field ligand. $ds{p}^2$, square planar, diamagnetic (all electrons paired). Correct.

Therefore, (i), (ii), and (iv) are correct.

The final answer is $\boxed{D}$