The correct answer is Option (1) → (A)-(III), (B)-(IV), (C)-(I), (D)-(II)
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List-I Complex
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List-II Number of unpaired electrons (n)
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(A) $[NiCl_4]^{2-}$
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(III) 2
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(B) $[Co(NH_3)_6]^{3+}$
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(IV) 0
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(C) $[FeF_6]^{3-}$
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(I) 5
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(D) $[Fe(CN)_6]^{3-}$
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(II) 1
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(A) $[NiCl_4]^{2-}$:
- Metal: $Ni^{2+}$ ($3d^8$).
- Ligand: $Cl^-$ is a weak field ligand and the geometry is tetrahedral.
- Configuration: In a tetrahedral field, the splitting is $e^4\,t_2^4$. There are 2 unpaired electrons.
- Match: (A) $\rightarrow$ (III)
(B) $[Co(NH_3)_6]^{3+}$:
- Metal: $Co^{3+}$ ($3d^6$).
- Ligand: $NH_3$ is a strong field ligand, leading to a low-spin octahedral complex.
- Configuration: $t_{2g}^6\,e_g^0$. All electrons are paired, so there are 0 unpaired electrons.
- Match: (B) $\rightarrow$ (IV)
(C) $[FeF_6]^{3-}$:
- Metal: $Fe^{3+}$ ($3d^5$).
- Ligand: $F^-$ is a weak field ligand, leading to a high-spin octahedral complex.
- Configuration: $t_{2g}^3\,e_g^2$. There are 5 unpaired electrons.
- Match: (C) $\rightarrow$ (I)
(D) $[Fe(CN)_6]^{3-}$:
- Metal: $Fe^{3+}$ ($3d^5$).
- Ligand: $CN^-$ is a strong field ligand, leading to a low-spin octahedral complex.
- Configuration: $t_{2g}^5\,e_g^0$. There is 1 unpaired electron.
- Match: (D) $\rightarrow$ (II)
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