Which of the following is a 4-carbon compound?

Options

A. Oxaloacetic acid
B. Phosphoglyceric acid
C. Oxalosuccinic acid
D. Phosphoenolpyruvate

Answer

To solve the question of which of the following is a 4-carbon compound, we will analyze each option provided:

1. **Oxaloacetic Acid**:
- This compound is known to be a key intermediate in the citric acid cycle (Krebs cycle) and is indeed a 4-carbon compound. It is formed from the condensation of carbon dioxide (1 carbon) with phosphoenolpyruvate (3 carbons), resulting in a total of 4 carbons.

2. **Phosphoglyceric Acid**:
- This compound is a product of the Calvin cycle and contains 3 carbon atoms. Therefore, it does not meet the criteria of being a 4-carbon compound.

3. **Oxalo-succinic Acid**:
- This compound is a derivative of oxaloacetic acid and is formed during certain metabolic processes. However, it contains 6 carbon atoms, which disqualifies it from being a 4-carbon compound.

4. **Phosphoenolpyruvate**:
- This is a 3-carbon compound that plays a crucial role in glycolysis and the Calvin cycle. Thus, it does not qualify as a 4-carbon compound.

After analyzing all the options, we conclude that the only 4-carbon compound among the options is **Oxaloacetic Acid**.

### Final Answer:
The correct answer is **Oxaloacetic Acid**.