Question

Find the correct match.

Column-I (Complex compound)	Column-II ($\Delta_0$ (CFSE) $\text{cm}^{-1}$)
(i) $[Cr(CN)_6]^{3-}$	(P) 17000
(ii) $[Cr(H_2O)_6]^{3+}$	(Q) 15000
(iii) $[Cr(en)_3]^{3+}$	(R) 12000
(iv) $[CrF_6]^{3-}$	(S) 20000

• (A) (i) → P ; (ii) → Q ; (iii) → S ; (iv) → R
• (B) (i) → S ; (ii) → Q ; (iii) → P ; (iv) → R
• (C) (i) → R ; (ii) → P ; (iii) → Q ; (iv) → S
• (D) (i) → P ; (ii) → R ; (iii) → Q ; (iv) → S

Answer 1

The Correct Option is B

Crystal Field Splitting Energy ($\Delta_0$) depends on the strength of the ligands according to the Spectrochemical Series.
1. Identify Ligand Strength:
The spectrochemical series order for these ligands is: $CN^- > en > H_2O > F^-$.

2. Relate to $\Delta_0$:
Stronger ligands cause greater splitting ($\Delta_0$). Therefore, the order of $\Delta_0$ values should be:
$[Cr(CN)_6]^{3-} > [Cr(en)_3]^{3+} > [Cr(H_2O)_6]^{3+} > [CrF_6]^{3-}$.

3. Match with numerical values:
Given values: 20000 (S) > 17000 (P) > 15000 (Q) > 12000 (R).
• (i) $[Cr(CN)_6]^{3-} \to 20000$ (S)
• (iii) $[Cr(en)_3]^{3+} \to 17000$ (P)
• (ii) $[Cr(H_2O)_6]^{3+} \to 15000$ (Q)
• (iv) $[CrF_6]^{3-} \to 12000$ (R)

4. Result: (i)-S, (ii)-Q, (iii)-P, (iv)-R. This matches option (B).