The first 5C dicarboxylic acid in Krebs' cycle which is used in nitrogen metabolism is

Options

A. OAA
B. citric acid
C. `alpha`-ketoglutaric acid
D. acetyl coenzyme A

Explanation

To solve the question regarding the first 5C dicarboxylic acid in the Krebs cycle that is used in nitrogen metabolism, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: We need to identify a 5-carbon dicarboxylic acid from the Krebs cycle that is also involved in nitrogen metabolism.

2. **Analyzing the Options**:
- **Option A: Oxaloacetic Acid**: This is a 4-carbon compound (C4) and therefore cannot be the answer.
- **Option B: Citric Acid**: This is a 6-carbon compound (C6) formed from oxaloacetic acid and acetyl-CoA, so it is also not the answer.
- **Option C: Alpha-Ketoglutaric Acid**: This is a 5-carbon compound (C5) and is known to be involved in nitrogen metabolism.
- **Option D: Acetyl-CoA**: This is a 2-carbon compound (C2) and is not relevant to the question.

3. **Identifying the Correct Answer**: Since alpha-ketoglutaric acid is the only 5-carbon dicarboxylic acid listed and is involved in nitrogen metabolism by converting into glutamate, it is the correct answer.

4. **Conclusion**: The first 5C dicarboxylic acid in the Krebs cycle that is used in nitrogen metabolism is **Alpha-Ketoglutaric Acid**.

### Final Answer:
**Alpha-Ketoglutaric Acid**

---