Question

Predict the magnetic nature of $K_2\left[Ni\right(CN{)}_4]$ (A) and $K_2\left[Ni\right(Cl{)}_4]$ (B)

• A. both are diamagnetic
• B. (A) is diamagnetic and (B) is paramagnetic with one unpaired electron
• C. (A) is diamagnetic and (B) is paramagnetic with two unpaired electrons
• D. both are paramagnetic

Answer 1

Answer: (C)

(A) is diamagnetic and (B) is paramagnetic with two unpaired electrons

Electronic configuraion of Ni in both compounds is $N{i}^{+2},3d^{8}4s^0$,
In case of $K_2\left[Ni\right(CN{)}_4]$, due to strong ligand pairing of electron happens and it has zero unpaired electron so diamagnetic.
In $K_2\left[Ni\right(Cl{)}_4]$, $C{l}^{-}$ is weak ligand so pairing of electron will not happen and it has two unpaired electron so it is paramagnetic.