Which one of the following is correct

Options

A. Azotobacter and Beijernikia are free living `N_(2)` -fixers
B. Rhodospirillum is anaerobic `N_(2)` fixing bacterium
C. Bacillus is a free living `N_(2)` fixer
D. All

Answer

To determine which statement is correct regarding nitrogen-fixing bacteria, we will analyze each option step by step.

### Step 1: Analyze the first statement
- **Statement**: Azotobacter and Bajanica are free-living nitrogen fixers.
- **Explanation**: Azotobacter is a well-known free-living nitrogen-fixing bacterium found in soil. Bajanica, often referred to as Bajanica or Bajanica sp., is also recognized for its nitrogen-fixing capabilities. Thus, this statement is correct.

### Step 2: Analyze the second statement
- **Statement**: Rhodospirillum is an anaerobic nitrogen-fixing bacterium.
- **Explanation**: Rhodospirillum is a genus of bacteria that can perform nitrogen fixation under anaerobic conditions. This statement is also correct.

### Step 3: Analyze the third statement
- **Statement**: Bacillus is a free-living nitrogen fixer.
- **Explanation**: Bacillus species, such as Bacillus subtilis, are known to fix nitrogen in a free-living state. Therefore, this statement is also correct.

### Step 4: Conclusion
- **Final Statement**: All the above statements are correct.
- **Explanation**: Since all individual statements about Azotobacter, Rhodospirillum, and Bacillus being nitrogen-fixing bacteria are correct, we conclude that the correct answer is option 4: All the above statements are correct.

### Final Answer
The correct answer is option 4: All the above statements are correct.

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