Question

Identify a lowest field strength ligand from following.

• A. \( I^{-} \)
• B. \( S^{2-} \)
• C. en
• D. CO

Hint:

Halide ions are generally weak-field ligands, while ligands that coordinate through Carbon or Nitrogen (like CO, CN, en) are strong-field ligands.

Answer 1

The Correct Option is A

Step 1: Concept
Ligands are arranged in the spectrochemical series based on their ability to cause crystal field splitting ($\Delta_o$).
Step 2: Spectrochemical Series
The common order is: $I^-<Br^-<S^{2-}<SCN^-<Cl^-<F^-<OH^-<ox^{2-}<H_2O<NCS^-<edta^{4-}<NH_3<en<CN^-<CO$.
Step 3: Analysis
Iodide ($I^-$) is at the extreme weak-field end of the series.
Step 4: Conclusion
Hence, $I^-$ is the lowest field strength ligand among the given options.
Final Answer:(A)