A good producer of citric acid is :

Options

A. Clostridium
B. Saccharomyces
C. Aspergillus
D. Pseudomonas

Answer

To determine a good producer of citric acid from the given options, we can analyze each option based on their known uses in microbial production.

### Step-by-Step Solution:

1. **Identify the Options**: The options provided are Clostridium, Saccharomyces, Aspergillus, and Pseudomonas.

2. **Analyze Clostridium**:
- Clostridium is primarily known for its role in the production of butyric acid.
- **Conclusion**: Clostridium is not a good producer of citric acid.

3. **Analyze Saccharomyces**:
- Saccharomyces is mainly used in the production of ethanol, particularly in fermentation processes like brewing and baking.
- **Conclusion**: Saccharomyces is not a good producer of citric acid.

4. **Analyze Aspergillus**:
- Aspergillus is a genus of fungi that is well-known for its ability to produce citric acid, especially Aspergillus niger.
- **Conclusion**: Aspergillus is a good producer of citric acid.

5. **Analyze Pseudomonas**:
- Pseudomonas is recognized for its role in the production of various compounds, including vitamin B12, but not citric acid.
- **Conclusion**: Pseudomonas is not a good producer of citric acid.

6. **Final Decision**:
- After analyzing all the options, the only organism that is a good producer of citric acid is **Aspergillus**.
- Therefore, the correct answer is **option number 3: Aspergillus**.