_____ is the 5C molecule of citric acid cycle.

Options

A. Succinic acid
B. Oxalosuccinic acid
C. alpha-ketoglutaric acid
D. Fumaric acid

Answer

To solve the question "_____ is the 5C molecule of the citric acid cycle," we need to identify the 5-carbon molecule that is part of the citric acid cycle (also known as the TCA cycle or tricarboxylic acid cycle).

### Step-by-Step Solution:

1. **Understand the Citric Acid Cycle**:
- The citric acid cycle is a series of chemical reactions used by aerobic organisms to release stored energy through the oxidation of acetyl-CoA.

2. **Identify the Options**:
- The question likely provides multiple-choice options. We will evaluate each option to find the 5-carbon molecule.

3. **Evaluate Each Option**:
- **Option 1: Succinic Acid**:
- Succinic acid is a 4-carbon molecule. Therefore, this option is incorrect.
- **Option 2: Oxalosuccinic Acid**:
- Oxalosuccinic acid is a 6-carbon molecule. Therefore, this option is also incorrect.
- **Option 3: Alpha-Ketoglutaric Acid**:
- Alpha-ketoglutaric acid is a 5-carbon molecule. It is formed by the decarboxylation of oxalosuccinic acid (which is a 6-carbon compound) in the presence of a decarboxylase enzyme. This option is correct.
- **Option 4: Fumaric Acid**:
- Fumaric acid is a 4-carbon molecule. Therefore, this option is incorrect.

4. **Conclusion**:
- After evaluating all the options, the correct answer is **Alpha-Ketoglutaric Acid**, which is the 5-carbon molecule of the citric acid cycle.

### Final Answer:
Alpha-Ketoglutaric Acid is the 5C molecule of the citric acid cycle.

---