Give the order of chelating effect of following ligands.
(i) `C_(2)O_(4)^(2-)` (ii) EDTA (iii) dien

Options

A. `iii gt ii gt i`
B. `i gt ii gt iii `
C. `ii gt iii gt i`
D. `igt iii gt ii `

Explanation

To determine the order of chelating effect of the given ligands, we need to analyze the number of donor atoms present in each ligand, as the chelating effect is directly related to the number of donor atoms.

### Step-by-Step Solution:

1. **Identify the Ligands:**
- The ligands given are:
- (i) Oxalate ion, \( C_2O_4^{2-} \)
- (ii) EDTA (Ethylenediaminetetraacetic acid)
- (iii) Diene (Diethylene triamine)

2. **Count the Donor Atoms:**
- **Oxalate ion \( C_2O_4^{2-} \):**
- The oxalate ion has two carboxylate groups (–COO⁻), each contributing one oxygen atom as a donor.
- Therefore, the total number of donor atoms in oxalate is **2**.

- **EDTA:**
- EDTA has a structure that includes two nitrogen atoms and four oxygen atoms (from the four carboxylate groups).
- Therefore, the total number of donor atoms in EDTA is **6** (2 from nitrogen and 4 from oxygen).

- **Diene (Diethylene triamine):**
- Diene contains three nitrogen atoms as donor atoms.
- Therefore, the total number of donor atoms in diene is **3**.

3. **Compare the Number of Donor Atoms:**
- Now we can compare the number of donor atoms for each ligand:
- Oxalate: 2 donor atoms
- Diene: 3 donor atoms
- EDTA: 6 donor atoms

4. **Determine the Order of Chelating Effect:**
- The chelating effect increases with the number of donor atoms. Therefore, the order of chelating effect from highest to lowest is:
- EDTA (6 donor atoms) > Diene (3 donor atoms) > Oxalate (2 donor atoms)

### Final Order:
**EDTA > Diene > Oxalate**