Which among the following ligands has highest field strength?

Step-by-step solution

The field strength of ligands follows the spectrochemical series , which ranks ligands by their ability to induce crystal field splitting ( ). Among the given ligands, carbonyl ( CO ) is a strong-field ligand positioned near the high-splitting end of the series. The approximate order for these ligands is OH ⁻ Since CO produces the largest crystal field splitting, it has the highest field strength.