Which of the following molecules or ions is a bidentate ligand ?

Options

A. `C_(2)O_(4)^(2-)`
B. `Br^(2+)`
C. `CH_(3)NH_(2)`
D. `CH_(3)-C-=N`

Explanation

To determine which of the given molecules or ions is a bidentate ligand, we first need to understand what a bidentate ligand is. A bidentate ligand is a molecule or ion that can donate two pairs of electrons (two lone pairs) to a metal atom or ion, forming two coordinate bonds.

### Step-by-Step Solution:

1. **Identify the Options**:
We need to look at the options provided in the question. For this example, let’s assume the options are:
- A) C2O4^2- (Oxalate ion)
- B) CH3NH2 (Methylamine)
- C) CH3CN (Acetonitrile)
- D) NH3 (Ammonia)

2. **Analyze Each Option**:
- **Option A: C2O4^2- (Oxalate ion)**:
- The oxalate ion has two oxygen atoms that can donate lone pairs to a metal center. Each of these oxygen atoms has a lone pair of electrons that can be used for bonding. Therefore, oxalate is a bidentate ligand.

- **Option B: CH3NH2 (Methylamine)**:
- Methylamine has one nitrogen atom that can donate a lone pair. It can only form one coordinate bond with a metal center, making it a monodentate ligand.

- **Option C: CH3CN (Acetonitrile)**:
- Acetonitrile has one nitrogen atom that can donate a lone pair. Similar to methylamine, it can only form one coordinate bond, thus it is also a monodentate ligand.

- **Option D: NH3 (Ammonia)**:
- Ammonia has one nitrogen atom that can donate a lone pair. It is also a monodentate ligand since it can only form one coordinate bond.

3. **Conclusion**:
After analyzing all the options, we find that the only bidentate ligand among the given choices is **C2O4^2- (Oxalate ion)**.

### Final Answer:
The bidentate ligand is **C2O4^2- (Oxalate ion)**.