Question

Given below are two statements: S-I: \( [\text{CoBr}_4]^{2-} \) absorbs lesser energy than \( [\text{CoCl}_4]^{2-} \) S-II: \( [\text{CoCl}_4]^{2-} \) has higher crystal field splitting energy than \( [\text{CoBr}_4]^{2-} \)

• A. Both S-I and S-II are correct
• B. Both S-I and S-II are incorrect
• C. S-I is correct and S-II is incorrect
• D. S-I is incorrect and S-II is correct

Hint:

Stronger field ligands cause larger crystal field splitting and require absorption of higher energy radiation.

Answer 1

The Correct Option is A

Concept:

Crystal field splitting energy (\( \Delta \)) depends on the nature of the ligand.
Stronger field ligands produce larger splitting.
According to the spectrochemical series: \[ \text{Br}^-<\text{Cl}^- \]
Energy absorbed during electronic transition is directly proportional to \( \Delta \).
Step 1: Compare the ligands \( \text{Cl}^- \) and \( \text{Br}^- \). Since \( \text{Cl}^- \) is a stronger field ligand than \( \text{Br}^- \), \[ \Delta_{\text{Cl}^-}>\Delta_{\text{Br}^-} \]
Step 2: Analyze Statement S-I. \[ [\text{CoBr}_4]^{2-} \text{ has smaller } \Delta \Rightarrow \text{absorbs lesser energy} \] Hence, Statement S-I is correct.
Step 3: Analyze Statement S-II. Since crystal field splitting energy is greater for stronger ligands: \[ \Delta_{[\text{CoCl}_4]^{2-}}>\Delta_{[\text{CoBr}_4]^{2-}} \] Hence, Statement S-II is also correct. Conclusion: Both S-I and S-II are correct.