Question:
Which of the following orders correctly represent the strength of ligands in the spectrochemical series?
I. $\text{I}^- \lt \text{Br}^- \lt \text{S}^{2-} \lt \text{SCN}^-$
II. $\text{H}_2\text{O} \lt \text{NCS}^- \lt \text{NH}_3 \lt \text{en}$
III. $\text{Cl}^- \lt \text{F}^- \lt \text{N}^{3-} \lt \text{OH}^-$
Which of the following orders correctly represent the strength of ligands in the spectrochemical series?
I. $\text{I}^- \lt \text{Br}^- \lt \text{S}^{2-} \lt \text{SCN}^-$
II. $\text{H}_2\text{O} \lt \text{NCS}^- \lt \text{NH}_3 \lt \text{en}$
III. $\text{Cl}^- \lt \text{F}^- \lt \text{N}^{3-} \lt \text{OH}^-$
I. $\text{I}^- \lt \text{Br}^- \lt \text{S}^{2-} \lt \text{SCN}^-$
II. $\text{H}_2\text{O} \lt \text{NCS}^- \lt \text{NH}_3 \lt \text{en}$
III. $\text{Cl}^- \lt \text{F}^- \lt \text{N}^{3-} \lt \text{OH}^-$
Show Hint
Remember the general order of donor atoms in the spectrochemical series to easily solve these questions:
$\text{Halogen donors} \lt \text{Oxygen donors} \lt \text{Nitrogen donors} \lt \text{Carbon donors}$.
$\text{Halogen donors} \lt \text{Oxygen donors} \lt \text{Nitrogen donors} \lt \text{Carbon donors}$.
Updated On: Jul 22, 2026
- I, II only
- II, III only
- I, III only
- I, II, III
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Question:
The question is from coordination chemistry.
We need to determine which of the given ligand strength orders are correct according to the spectrochemical series.
Step 2: Key Formula or Approach:
The spectrochemical series arranges ligands in order of increasing crystal field splitting energy ($\Delta_{\text{o}}$ value):
\( \text{I}^- \lt \text{Br}^- \lt \text{S}^{2-} \lt \text{SCN}^- \lt \text{Cl}^- \lt \text{N}_3^- \lt \text{F}^- \lt \text{OH}^- \lt \text{C}_2\text{O}_4^{2-} \lt \text{H}_2\text{O} \lt \text{NCS}^- \lt \text{EDTA}^{4-} \lt \text{NH}_3 \lt \text{en} \lt \text{CN}^- \lt \text{CO} \)
Step 3: Detailed Explanation:
• Let us evaluate each proposed order:
• Order I: $\text{I}^- \lt \text{Br}^- \lt \text{S}^{2-} \lt \text{SCN}^-$
Comparing with the standard spectrochemical series, this order is correct. Halide ions are weak field ligands, and their field strength increases as their size decreases, with sulfur-donor ligands like sulfide and thiocyanate being slightly stronger.
• Order II: $\text{H}_2\text{O} \lt \text{NCS}^- \lt \text{NH}_3 \lt \text{en}$
This order is also correct. Water is weaker than nitrogen-donor ligands like isothiocyanate, ammonia, and ethylenediamine (which is a strong bidentate chelating ligand).
• Order III: $\text{Cl}^- \lt \text{F}^- \lt \text{N}^{3-} \lt \text{OH}^-$
This order is incorrect. Fluoride ($\text{F}^-$) is a weaker ligand than hydroxide ($\text{OH}^-$) in the spectrochemical series. The correct relative order is $\text{Cl}^- \lt \text{F}^- \lt \text{OH}^-$.
• Therefore, only orders I and II are correct.
Step 4: Final Answer:
The correct orders are I and II only.
The question is from coordination chemistry.
We need to determine which of the given ligand strength orders are correct according to the spectrochemical series.
Step 2: Key Formula or Approach:
The spectrochemical series arranges ligands in order of increasing crystal field splitting energy ($\Delta_{\text{o}}$ value):
\( \text{I}^- \lt \text{Br}^- \lt \text{S}^{2-} \lt \text{SCN}^- \lt \text{Cl}^- \lt \text{N}_3^- \lt \text{F}^- \lt \text{OH}^- \lt \text{C}_2\text{O}_4^{2-} \lt \text{H}_2\text{O} \lt \text{NCS}^- \lt \text{EDTA}^{4-} \lt \text{NH}_3 \lt \text{en} \lt \text{CN}^- \lt \text{CO} \)
Step 3: Detailed Explanation:
• Let us evaluate each proposed order:
• Order I: $\text{I}^- \lt \text{Br}^- \lt \text{S}^{2-} \lt \text{SCN}^-$
Comparing with the standard spectrochemical series, this order is correct. Halide ions are weak field ligands, and their field strength increases as their size decreases, with sulfur-donor ligands like sulfide and thiocyanate being slightly stronger.
• Order II: $\text{H}_2\text{O} \lt \text{NCS}^- \lt \text{NH}_3 \lt \text{en}$
This order is also correct. Water is weaker than nitrogen-donor ligands like isothiocyanate, ammonia, and ethylenediamine (which is a strong bidentate chelating ligand).
• Order III: $\text{Cl}^- \lt \text{F}^- \lt \text{N}^{3-} \lt \text{OH}^-$
This order is incorrect. Fluoride ($\text{F}^-$) is a weaker ligand than hydroxide ($\text{OH}^-$) in the spectrochemical series. The correct relative order is $\text{Cl}^- \lt \text{F}^- \lt \text{OH}^-$.
• Therefore, only orders I and II are correct.
Step 4: Final Answer:
The correct orders are I and II only.
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