Name two free living `N_2` - fixing bacteria.

Explanation

**Step-by-Step Solution:**

1. **Understanding Nitrogen Fixation**: Nitrogen fixation is the process by which nitrogen (N2) in the atmosphere is converted into ammonia (NH3) or related compounds in soil. This process is crucial for the growth of plants as they require nitrogen for their development.

2. **Identifying Free-Living Nitrogen-Fixing Bacteria**: Free-living nitrogen-fixing bacteria are those that do not form symbiotic relationships with plants. They can independently fix nitrogen from the atmosphere and are typically found in soil.

3. **Naming Two Free-Living Nitrogen-Fixing Bacteria**:
- **Azotobacter**: This is a genus of free-living bacteria that can fix nitrogen. They are commonly found in soil and are known for their ability to thrive in aerobic conditions.
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