.................is a symbiotic `N_2` fixer while ................... is a free living soil `N_2` fixer.

Explanation

To answer the question, we need to identify two types of nitrogen-fixing bacteria: one that is symbiotic and one that is free-living.

1. **Identify Symbiotic Nitrogen Fixer**:
- Symbiotic nitrogen fixers are bacteria that form a mutual relationship with plants, particularly legumes.
- The most well-known symbiotic nitrogen fixer is **Rhizobium**. This bacterium lives in the root nodules of leguminous plants (like lentils and peas) and helps convert atmospheric nitrogen into a form that the plant can use.

2. **Identify Free-Living Nitrogen Fixer**:
- Free-living nitrogen fixers are bacteria that do not form a symbiotic relationship with plants. They exist independently in the soil and can fix nitrogen on their own.
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