Name two free-living nitrogen-fixing bacteria.

Explanation

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**:
- Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into a form that plants can use, such as ammonia (NH₃). This process is essential for plant growth as nitrogen is a crucial nutrient.

2. **Identify Types of Nitrogen-Fixing Bacteria**:
- Nitrogen-fixing bacteria can be categorized into two main types:
- **Free-living bacteria**: These bacteria do not depend on other organisms for their survival.
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