Which of the following ligands does form a chelate ?

Options

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

Explanation

To determine which ligand forms a chelate, we need to understand the concept of chelation and the types of ligands involved.

### Step-by-Step Solution:

1. **Understand Chelation**: Chelation refers to the formation of a complex where a ligand binds to a metal ion at multiple points, forming a ring structure. These ligands are typically bidentate or polydentate.

2. **Identify the Types of Ligands**:
- **Monodentate Ligands**: These ligands can bind to a metal ion at only one site. Examples include acetate (CH3COO-), cyanide (CN-), and ammonia (NH3).
- **Bidentate Ligands**: These ligands can bind to a metal ion at two sites, allowing for the formation of a chelate. An example is oxalate (C2O4^2-).

3. **Analyze the Given Ligands**:
- **Acetate (CH3COO-)**: This is a monodentate ligand as it can only bind through one oxygen atom.
- **Oxalate (C2O4^2-)**: This is a bidentate ligand as it can bind through two oxygen atoms.
- **Cyanide (CN-)**: This is a monodentate ligand as it can only bind through the carbon atom.
- **Ammonia (NH3)**: This is also a monodentate ligand as it can only bind through the nitrogen atom.

4. **Determine Which Ligands Form Chelates**:
- From the analysis, only oxalate is a bidentate ligand that can form a chelate. The other ligands (acetate, cyanide, and ammonia) are monodentate and do not form chelates.

5. **Conclusion**: The ligand that forms a chelate among the given options is **oxalate (C2O4^2-)**.

### Final Answer:
The ligand that forms a chelate is **oxalate (C2O4^2-)**.