Question

Which of the following is a correct increasing order of ligand field strength ?

• A. \(\text{EDTA} < \text{C}_2\text{O}_4^{2-} < \text{H}_2\text{O} < \text{en}\)
• B. \(\text{en} < \text{H}_2\text{O} < \text{EDTA} < \text{C}_2\text{O}_4^{2-}\)
• C. \(\text{C}_2\text{O}_4^{2-} < \text{H}_2\text{O} < \text{EDTA} < \text{en}\)
• D. \(\text{H}_2\text{O} < \text{en} < \text{C}_2\text{O}_4^{2-} < \text{EDTA}\)

Hint:

Spectrochemical series order here: oxalate < water < EDTA < en.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The spectrochemical series arranges ligands by the size of the crystal field splitting they cause. A stronger field ligand gives a larger splitting.

Step 2: Key Formula or Approach:
In the common spectrochemical series the relevant ligands appear in this increasing order:
\[ \text{C}_2\text{O}_4^{2-} < \text{H}_2\text{O} < \text{EDTA}^{4-} < \text{en} \]
Oxygen donors such as oxalate and water are weak. EDTA (mixed N and O donors) is stronger. Ethylenediamine (N donors) is stronger still.

Step 3: Detailed Explanation:
Compare each option with this order.
(A) places EDTA first, which contradicts the series where EDTA is stronger than oxalate and water.
(B) starts with en as the weakest, but en is the strongest of the four.
(D) puts water as the weakest, but oxalate is weaker than water.
(C) lists oxalate, then water, then EDTA, then en, which matches the series.

Final Answer:
The increasing order of ligand field strength is oxalate, water, EDTA, en, option (C). \[ \boxed{\text{C}_2\text{O}_4^{2-}<\text{H}_2\text{O}<\text{EDTA}<\text{en} \text{ (C)}} \]