Which of the following is the correct order of increasing field strength of ligands to form coordination compounds?

Options

A. `SCN^(-)ltF^(-)ltC_2O_4^(2-)ltCN^(-)`
B. `SCN^(-) lt F^(-) lt CN^(-) lt C_2O_4^(2-)`
C. `F^(-) lt SCN^(-) lt C_2O_4^(2-) lt CN^(-)`
D. `CN^(-) lt C_2O_4^(2-) lt SCN^(-) lt F^(-)`

Answer

To determine the correct order of increasing field strength of ligands to form coordination compounds, we will refer to the Spectrochemical series, which ranks ligands based on their ability to split the d-orbitals of transition metal ions.

### Step-by-Step Solution:

1. **Understand Ligand Field Strength**: Ligands can be classified as strong field or weak field based on their ability to cause splitting of d-orbitals in transition metals. Strong field ligands cause a large splitting, while weak field ligands cause a small splitting.

2. **Refer to the Spectrochemical Series**: The Spectrochemical series lists ligands in order of increasing field strength. The general order from weak to strong field ligands is as follows:
- Iodide (I⁻) < Bromide (Br⁻) < Thiocyanate (SCN⁻) < Chloride (Cl⁻) < Sulfide (S²⁻) < Azide (N₃⁻) < Fluoride (F⁻) < Hydroxide (OH⁻) < Oxalate (C₂O₄²⁻) < Water (H₂O) < Thiocyanate (NCS⁻) < Ethylenediaminetetraacetic acid (EDTA⁴⁻) < Ammonia (NH₃) < Pyridine < Bipyridine < Phenyl < Nitrite (NO₂⁻) < Cyanide (CN⁻).

3. **Identify the Ligands in the Question**: Based on the options provided, identify the ligands mentioned in the question. For example, if the ligands are CN⁻, C₂O₄²⁻, and F⁻, we need to find their positions in the Spectrochemical series.

4. **Rank the Ligands**:
- CN⁻ is a strong field ligand.
- C₂O₄²⁻ is also a strong field ligand but weaker than CN⁻.
- F⁻ is a weak field ligand.

5. **Determine the Order of Increasing Field Strength**: Based on the positions in the Spectrochemical series, the order of increasing field strength is:
- F⁻ < C₂O₄²⁻ < CN⁻.

6. **Match with Options**: Finally, compare this order with the provided options to identify the correct one.

### Conclusion:
The correct order of increasing field strength of the ligands is:
**F⁻ < C₂O₄²⁻ < CN⁻**.