Question

The correct sequence of ligands in the order of decreasing field strength is :

• A. \( \text{CO} > \text{H}_2\text{O} > \text{F}^- > \text{S}^{2-} \)
• B. \( \text{OH}^- > \text{F}^- > \text{NH}_3 > \text{CN}^- \)
• C. \( \text{NCS}^- > \text{EDTA}^{4-} > \text{CN}^- > \text{CO} \)
• D. \( \text{S}^{2-} > \text{OH}^- > \text{EDTA}^{4-} > \text{CO} \)

Answer 1

The Correct Option is A

Understanding Ligand Field Strength:

The strength of a ligand in the context of field strength refers to its ability to split the \(d\)-orbitals of a transition metal ion, which affects the color, magnetic properties, and stability of the metal complex. Ligands are arranged according to their field strength in the Spectrochemical Series.

Spectrochemical Series:

According to the Spectrochemical Series, ligands are arranged in the following order of increasing field strength:

\[ I^- < \text{Br}^- < S^{2-} < \text{Cl}^- < \text{F}^- < \text{OH}^- < \text{H}_2\text{O} < \text{NCS}^- < \text{EDTA}^{4-} < \text{NH}_3 < \text{en} < \text{CN}^- < \text{CO} \]

Arrange the Given Ligands in Decreasing Field Strength:

From the Spectrochemical Series:

\[ \text{CO} > \text{H}_2\text{O} > \text{F}^- > S^{2-} \]

Conclusion:

The correct sequence in the order of decreasing field strength is:

\[ \text{CO} > \text{H}_2\text{O} > \text{F}^- > S^{2-} \]

which corresponds to Option (1).

Answer 2

Step 1: Given information.
Sequence needed: Arrange the ligands \( \text{CO} \), \( \text{H}_2\text{O} \), \( \text{F}^- \), \( \text{S}^{2-} \) in order of decreasing field strength.

Step 2: Concept – Spectrochemical series.
The spectrochemical series arranges ligands from weak field to strong field based on their ability to cause crystal field splitting (\( \Delta_0 \)).
General field strength order in the series is:
\( \text{I}^- < \text{Br}^- < \text{S}^{2-} < \text{F}^- < \text{H}_2\text{O} < \text{NH}_3 < \text{NO}_2^- < \text{CN}^- < \text{CO} \)

Step 3: Arrange the given ligands.
From the series:
- \( \text{CO} \) (strongest)
- \( \text{H}_2\text{O} \) (moderate field)
- \( \text{F}^- \) (weak field)
- \( \text{S}^{2-} \) (very weak field)
Therefore, the sequence in decreasing field strength is:
\( \text{CO} > \text{H}_2\text{O} > \text{F}^- > \text{S}^{2-} \)

Step 4: Final Answer.
\( \boxed{\text{CO} > \text{H}_2\text{O} > \text{F}^- > \text{S}^{2-}} \)