Photosynthetic prokaryotic organism is:-

Options

A. Rhizobium
B. Nostoc
C. Pseudomonas
D. Staphylococcus

Answer

To determine which of the given options is a photosynthetic prokaryotic organism, we can analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Prokaryotic Organisms**:
- Prokaryotic organisms are unicellular organisms that lack a nucleus. They include bacteria and archaea.

2. **Identifying Photosynthetic Organisms**:
- Photosynthetic organisms are those that can convert light energy into chemical energy through the process of photosynthesis.

3. **Analyzing the Options**:
- **Option 1: Rhizobium**
- Rhizobium is a type of bacteria known for its role in nitrogen fixation in legumes. It does not perform photosynthesis.
- **Conclusion**: This option is incorrect.

- **Option 2: Nostoc**
- Nostoc is a genus of cyanobacteria (also known as blue-green algae) that can perform photosynthesis. They are prokaryotic and capable of fixing nitrogen as well.
- **Conclusion**: This option is correct.

- **Option 3: Pseudomonas**
- Pseudomonas is a genus of bacteria that are primarily known for their role in processes like denitrification and are not photosynthetic.
- **Conclusion**: This option is incorrect.

- **Option 4: Staphylococcus**
- Staphylococcus is a genus of gram-positive bacteria that are round-shaped and do not perform photosynthesis.
- **Conclusion**: This option is incorrect.

4. **Final Answer**:
- Based on the analysis, the photosynthetic prokaryotic organism among the options provided is **Nostoc** (Option 2).

### Summary:
The correct answer to the question "Photosynthetic prokaryotic organism is:" is **Nostoc**.