JEE Main 2026 — Jan 28, Shift 1 — Chemistry solution

JEE Main2026Jan 28, Shift 1Chemistry

The correct statement among the following is:

A
$[Ni(CN)_{4}]^{2 -}$ and $[NiCl_{4}]^{2 -}$ are diamagnetic and Ni(CO) $_{4}$ is paramagnetic.
B
Ni(CO) $_{4}$ and $[NiCl_{4}]^{2 -}$ are diamagnetic and $[Ni(CN)_{4}]^{2 -}$ is paramagnetic.
C
Ni(CO) $_{4}$ and $[Ni(CN)_{4}]^{2 -}$ are diamagnetic and $[NiCl_{4}]^{2 -}$ is paramagnetic.
D
Ni(CO) $_{4}$ is diamagnetic and $[NiCl_{4}]^{2 -}$ and $[Ni(CN)_{4}]^{2 -}$ are paramagnetic.

Solution

Determine the electron configuration and geometry of each Ni complex.

Ni(CO) $_{4}$ : Ni is in oxidation state 0, configuration 3d $^{10}$ after pairing under strong-field CO ligands. Geometry sp $^{3}$ , all electrons paired $\Rightarrow$ diamagnetic.

$[Ni(CN)_{4}]^{2 -}$ : Ni $^{2 +}$ is 3d $^{8}$ . CN $^{-}$ is a strong-field ligand causing pairing; geometry dsp $^{2}$ (square planar), all paired $\Rightarrow$ diamagnetic.

$[NiCl_{4}]^{2 -}$ : Ni $^{2 +}$ is 3d $^{8}$ . Cl $^{-}$ is weak-field; geometry sp $^{3}$ (tetrahedral) with two unpaired electrons $\Rightarrow$ paramagnetic.

$∴$ Ni(CO) $_{4}$ and $[Ni(CN)_{4}]^{2 -}$ are diamagnetic; $[NiCl_{4}]^{2 -}$ is paramagnetic. Option (3).

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