The non - symbiotic anaerobic nitrogen fixer is

Options

A. Rhizobium
B. Beijerinckia
C. Azotobacter
D. None of these

Answer

To solve the question regarding the non-symbiotic anaerobic nitrogen fixer, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**: Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related compounds in soil and water, making it available for living organisms.

2. **Identify Types of Nitrogen Fixers**: Nitrogen-fixing microorganisms can be categorized into two groups:
- **Symbiotic Nitrogen Fixers**: These organisms form a symbiotic relationship with plants (e.g., Rhizobium).
- **Non-symbiotic (Free-living) Nitrogen Fixers**: These organisms live independently in the soil and do not form relationships with plants.

3. **Focus on Anaerobic Conditions**: The question specifically asks for non-symbiotic anaerobic nitrogen fixers. Anaerobic organisms do not require oxygen for their metabolic processes.

4. **Evaluate the Options**: The options provided in the question are:
- **Rhizobium**: A symbiotic nitrogen fixer that requires oxygen.
- **Bacillus**: A free-living aerobic nitrogen fixer.
- **Azotobacter**: A free-living nitrogen fixer that operates under aerobic conditions.
- **Rhodospirillum**: A non-symbiotic anaerobic nitrogen fixer.

5. **Select the Correct Answer**: From the evaluation, it is clear that Rhodospirillum is the only option that fits the criteria of being a non-symbiotic anaerobic nitrogen fixer.

### Final Answer:
The non-symbiotic anaerobic nitrogen fixer is **Rhodospirillum**.

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