Which of the following is a tridentate ligand?

Options

A. `EDTA^(4-)`
B. `(CO O)_(2)^(2-)`
C. dien
D. `NO_(2)^(-)`

Explanation

To determine which of the following is a tridentate ligand, we need to understand the concept of denticity in coordination chemistry. Denticity refers to the number of donor atoms in a ligand that can coordinate to a central metal atom.

### Step-by-Step Solution:

1. **Understanding Denticity**:
- Denticity is defined as the number of donor atoms in a ligand that can bind to a central metal ion. A ligand can be classified based on its denticity:
- Monodentate (1 donor atom)
- Bidentate (2 donor atoms)
- Tridentate (3 donor atoms)
- Hexadentate (6 donor atoms), etc.

2. **Identifying the Ligands**:
- We need to analyze the ligands provided in the question to determine their denticity.
- The ligands mentioned are:
1. EDTA (Ethylenediaminetetraacetic acid)
2. Oxalate
3. Diethylene triamine (Dien)
4. Nitrite (NO2^-)

3. **Analyzing Each Ligand**:
- **EDTA**: This ligand has six donor atoms (four carboxylate groups and two amine groups), making it hexadentate.
- **Oxalate**: This ligand has two donor atoms (two carboxylate groups), making it bidentate.
- **Diethylene triamine (Dien)**: This ligand has three nitrogen atoms, each capable of donating a lone pair of electrons to the metal ion. Therefore, it is a tridentate ligand.
- **Nitrite (NO2^-)**: This ligand has one donor atom (the nitrogen), making it monodentate.

4. **Conclusion**:
- Among the ligands analyzed, **Diethylene triamine (Dien)** is the only tridentate ligand, as it has three donor atoms (the three nitrogen atoms).

### Final Answer:
The tridentate ligand among the options provided is **Diethylene triamine (Dien)**.

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