A free - living soil bacterium capable of `N_(2)` fixation is

Options

A. Rhizobium
B. Azotobacter
C. Streptococcus
D. Anabaena

Answer

To solve the question about a free-living soil bacterium capable of nitrogen fixation, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process by which certain bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃) or related compounds, making nitrogen available for plants.

2. **Types of Nitrogen-Fixing Bacteria**:
- There are two main types of nitrogen-fixing bacteria:
- **Symbiotic bacteria**: These bacteria live in association with plant roots (e.g., Rhizobium, which forms root nodules with legumes).
- **Free-living bacteria**: These bacteria do not require a plant host and can fix nitrogen independently from the environment.

3. **Identifying Free-Living Nitrogen-Fixing Bacteria**:
- Among the bacteria mentioned in the question, we need to identify which one is free-living.
- **Rhizobium** and **Anabaena** are known for forming symbiotic relationships with plants, while **Streptococcus** is not typically involved in nitrogen fixation.

4. **Identifying the Correct Answer**:
- The correct answer is **Azotobacter**, which is a free-living bacterium capable of fixing nitrogen directly from the atmosphere without the need for a plant host.

### Final Answer:
The free-living soil bacterium capable of nitrogen fixation is **Azotobacter**.