Question

Identify the correct increasing order of field strength of ligands from following.

• A. $Cl^- < I^- < S^{2-} < OH^-$
• B. $I^- < Cl^- < S^{2-} < OH^-$
• C. $OH^- < Cl^- < I^- < S^{2-}$
• D. $S^{2-} < OH^- < I^- < Cl^-$

Hint:

A general rule of thumb for ligand field strength is based on the donor atom:
Halogen donors < Oxygen/Sulfur donors < Nitrogen donors < Carbon donors.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks us to arrange four specific ligands in order of their increasing crystal field splitting capability based on the spectrochemical series.

Step 2: Detailed Explanation:
The spectrochemical series is an experimentally determined list of ligands arranged based on their ability to split the d-orbital energy levels of the central metal ion ($\Delta_o$).
According to standard textbook spectrochemical series (e.g., NCERT), the established increasing order for common ligands is:
$I^- < Br^- < SCN^- < Cl^- < S^{2-} < F^- < OH^- < C_2O_4^{2-} < H_2O < NCS^- < edta^{4-} < NH_3 < en < CN^- < CO$
From this exact experimental sequence, we can isolate the relative positions of the four ligands in question:
- Iodide ($I^-$) is the weakest field ligand among them.
- Chloride ($Cl^-$) is slightly stronger than Iodide but weaker than Sulfide.
- Sulfide ($S^{2-}$) comes next.
- Hydroxide ($OH^-$) is the strongest field ligand in this specific subset.
Therefore, the correct extracted sequence must be:
$I^- < Cl^- < S^{2-} < OH^-$

Step 3: Final Answer:
The strictly correct order corresponds perfectly to option (b).