Non-symbiotic nitrogen fixing prokaryote is

Options

A. Frankia
B. Azotobacter
C. Rhizobium
D. Nostoc

Answer

To determine the non-symbiotic nitrogen-fixing prokaryote from the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for a non-symbiotic nitrogen-fixing prokaryote. Non-symbiotic nitrogen-fixing bacteria are those that do not form a symbiotic relationship with plants.

2. **Identify the Options**: The options provided are:
- A) Frankia
- B) Azotobacter
- C) Rhizobium
- D) Nostoc

3. **Define Non-symbiotic Nitrogen Fixation**: Non-symbiotic nitrogen-fixing bacteria are free-living bacteria that can fix atmospheric nitrogen into ammonia without the need for a host plant.

4. **Analyze Each Option**:
- **Frankia**: This is a nitrogen-fixing actinobacteria that forms symbiotic relationships with certain plants (e.g., alder trees). Therefore, it is not a non-symbiotic nitrogen fixer.
- **Azotobacter**: This is a free-living nitrogen-fixing bacterium that does not require a plant host to fix nitrogen. It is indeed a non-symbiotic nitrogen fixer.
- **Rhizobium**: This bacterium forms symbiotic relationships with legumes, hence it is not a non-symbiotic nitrogen fixer.
- **Nostoc**: This is a cyanobacterium that can also form symbiotic relationships with plants, although it can exist freely in some cases. However, it is not primarily classified as a non-symbiotic nitrogen fixer.

5. **Conclusion**: Based on the analysis, the only option that fits the criteria of a non-symbiotic nitrogen-fixing prokaryote is **B) Azotobacter**.

### Final Answer:
**B) Azotobacter**