Question

Identify weak field ligand from following.

• A. $NH_{3}$
• B. $CN^{-}$
• C. $Br^{-}$
• D. $CO$

Hint:

Weak field ligands usually cause low crystal field splitting and form high-spin complexes.

Answer 1

The Correct Option is C

Step 1: Concept
The strength of ligands is determined by the Spectrochemical Series.

Step 2: Analysis
General order of strength: $I^{-} < Br^{-} < Cl^{-} < F^{-} < OH^{-} < H_{2}O < NH_{3} < en < CN^{-} < CO$

Step 3: Comparison
- $CN^{-}$ and $CO$ are very strong field ligands. - $NH_{3}$ is a moderate/strong field ligand. - Halide ions ($Br^{-}$) are weak field ligands.

Step 4: Conclusion
Hence, $Br^{-}$ is the weak field ligand. Final Answer: (C)