From the magnetic behaviour of $\left[\mathrm{NiCl}_{4}\right]^{2-}$ (paramagnetic) and $\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]$ (diamagnetic), choose the correct geometry and oxidation state.

(B) $\left[\mathrm{NiCl}_{4}\right]^{2-}: \mathrm{Ni}^{\mathrm{II}}$, tetrahedral $\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]: \mathrm{Ni}(0)$, tetrahedral

(A) $\left[\mathrm{NiCl}_{4}\right]^{2-}: \mathrm{Ni}^{\mathrm{II}}$, square planar $\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]: \mathrm{Ni}(0)$, square planar

(C) $\left[\mathrm{NiCl}_{4}\right]^{2-}: \mathrm{Ni}^{\mathrm{II}}$, tetrahedral $\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]: \mathrm{Ni}^{\mathrm{II}}$, square planar

(D) $\left[\mathrm{NiCl}_{4}\right]^{2-}: \mathrm{Ni}(0)$, tetrahedral $\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]: \mathrm{Ni}(0)$, square planar

JEE Main · 2025 · 22 Jan 2025 · Shift 1 · Coordination Compounds

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From the magnetic behaviour of

[NiCl_{4}]^{2 -}

(paramagnetic) and

[Ni (CO)_{4}]

(diamagnetic), choose the correct geometry and oxidation state.

(A) $[NiCl_{4}]^{2 -} : Ni^{II}$ , square planar
$[Ni (CO)_{4}] : Ni (0)$ , square planar
(B) $[NiCl_{4}]^{2 -} : Ni^{II}$ , tetrahedral
$[Ni (CO)_{4}] : Ni (0)$ , tetrahedral✓ Correct
(C) $[NiCl_{4}]^{2 -} : Ni^{II}$ , tetrahedral
$[Ni (CO)_{4}] : Ni^{II}$ , square planar
(D) $[NiCl_{4}]^{2 -} : Ni (0)$ , tetrahedral
$[Ni (CO)_{4}] : Ni (0)$ , square planar

Answer: (B)

Solution

[N i C l_{4}]^{2 -}

, nickel is

N i^{2 +}

[A r] 3 d^{8}

C l^{-}

is a weak-field ligand, so the complex adopts

s p^{3}

hybridisation and tetrahedral geometry, retaining two unpaired

d

-electrons — consistent with its observed paramagnetism.

In

[N i (C O)_{4}]

, nickel is in the zero oxidation state,

[A r] 3 d^{10}

once the

4 s

electrons redistribute into

d

. With a full

d^{10}

shell all electrons are paired, and the complex is again

s p^{3}

, tetrahedral — consistent with its diamagnetism.

[N i C l_{4}]^{2 -}

N i^{I I}

, tetrahedral, and

[N i (C O)_{4}]

N i (0)

, tetrahedral.

JEE Main · 2025 · 22 Jan 2025 · Shift 1 · Single correct option

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JEE Main · 2025 · 22 Jan 2025 · Shift 1 · Coordination Compounds

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