`N_(2)` fixation is

Options

A. `N_(2) to NH_(3)`
B. `NO_(3) to NO_(2)`
C. `N_(2) to `amino acid
D. both (1) and (2)

Answer

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**: Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related compounds. This is essential for making nitrogen available to plants, as they cannot utilize atmospheric nitrogen directly.

2. **Chemical Conversion**: The primary reaction in nitrogen fixation can be summarized as:
\[ N_2 + 3H_2 \rightarrow 2NH_3 \]
This reaction shows that nitrogen gas combines with hydrogen to form ammonia.

3. **Role of Bacteria**: Certain bacteria play a crucial role in nitrogen fixation. Notable examples include:
- **Rhizobium**: These bacteria form symbiotic relationships with leguminous plants, fixing nitrogen in root nodules.
- **Azotobacter**: These are free-living nitrogen-fixing bacteria found in the soil.

4. **Subsequent Processes**: After nitrogen fixation, ammonia can be further processed into nitrates (NO₃⁻) through nitrification, which involves:
- Conversion of ammonia to nitrites (NO₂⁻) by bacteria such as Nitrosomonas.
- Conversion of nitrites to nitrates by bacteria such as Nitrobacter.

5. **Importance of Nitrogen Compounds**: The nitrogen compounds produced (like ammonia and nitrates) are vital for plant growth as they are incorporated into amino acids and proteins.

6. **Conclusion**: Therefore, nitrogen fixation is primarily the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃), which is essential for plant nutrition.