Which of the following ligands forms chelate with metal ion?

Options

A. Acetate
B. Oxalate
C. Cyanide
D. Ammonia

Answer

To determine which ligand forms a chelate with a metal ion, we need to understand the concept of chelation and identify the nature of the ligands provided.

### Step-by-Step Solution:

1. **Understanding Chelation:**
- Chelation is the process where a ligand binds to a metal ion through multiple coordination sites, forming a ring structure. This is typically done by bidentate or polydentate ligands.

2. **Identifying the Ligands:**
- We need to analyze the given ligands to see if they can form chelates. The ligands mentioned are:
- Acetate (CH3COO-)
- Oxalate (C2O4^2-)
- Cyanide (CN-)
- Ammonia (NH3)

3. **Analyzing Acetate:**
- Acetate is a monodentate ligand, meaning it can coordinate with a metal ion at only one site. Therefore, it cannot form a ring structure and does not exhibit chelation.

4. **Analyzing Oxalate:**
- Oxalate is a bidentate ligand, as it has two coordination sites that can bind to a metal ion. When oxalate coordinates with a metal, it can form a ring structure, thus exhibiting chelation.

5. **Analyzing Cyanide:**
- Cyanide is also a monodentate ligand, coordinating at only one site. Therefore, it cannot form a chelate.

6. **Analyzing Ammonia:**
- Ammonia is another example of a monodentate ligand. It can only coordinate with a metal ion at one site and cannot form a chelate.

7. **Conclusion:**
- Among the ligands analyzed, only oxalate can form a chelate with a metal ion due to its ability to bind through two coordination sites and form a ring structure.

### Final Answer:
The ligand that forms a chelate with a metal ion is **Oxalate (C2O4^2-)**.