Which of the following is a free living nitrogen fixing bacteria ?

Options

A. Rhizobium
B. Azotobacter
C. Nitrococcus
D. Both (1 ) & (2)

Answer

To answer the question "Which of the following is a free-living nitrogen-fixing bacteria?" we will analyze the options provided and understand the characteristics of nitrogen-fixing bacteria.

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process where atmospheric nitrogen (N₂) is converted into ammonia (NH₃) by certain organisms. This is crucial for the nitrogen cycle and for providing usable nitrogen to plants.

2. **Types of Nitrogen Fixers**:
- There are two main types of nitrogen-fixing bacteria:
- **Free-living nitrogen fixers**: These bacteria live independently in the soil and do not form symbiotic relationships with plants.
- **Symbiotic nitrogen fixers**: These bacteria form symbiotic relationships with specific plants, such as legumes.

3. **Analyzing the Options**:
- **Rhizobium**: This is a well-known symbiotic nitrogen-fixing bacteria that forms nodules on the roots of leguminous plants. Therefore, it is not a free-living nitrogen fixer.
- **Azotobacter**: This is a free-living nitrogen-fixing bacterium that can be found in the soil and does not require a plant host for its nitrogen-fixing activity.
- **Nitrococcus**: This is not a nitrogen-fixing bacterium; instead, it is a nitrifying bacterium that converts ammonia into nitrite (NO₂⁻).

4. **Conclusion**:
- Based on the analysis, the only free-living nitrogen-fixing bacteria among the options is **Azotobacter**.

### Final Answer:
The correct answer is **Azotobacter**.

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