Match the complex given in List-I with the number of unpaired electro…

The correct answer is Option (1) → (A)-(III), (B)-(IV), (C)-(I), (D)-(II)

List-I Complex	List-II Number of unpaired electrons (n)
(A) $[NiCl_4]^{2-}$	(III) 2
(B) $[Co(NH_3)_6]^{3+}$	(IV) 0
(C) $[FeF_6]^{3-}$	(I) 5
(D) $[Fe(CN)_6]^{3-}$	(II) 1

(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)