The first stable product of biological nitrogen fixation is:

Options

A. Nitrate
B. Nitrite
C. Ammonia
D. Amino acid

Answer

### Step-by-Step Solution:

1. **Understanding Biological Nitrogen Fixation**:
- Biological nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into a form that plants can use, primarily ammonia (NH₃). This process is facilitated by certain bacteria, including those that are symbiotic with plants (like Rhizobium) and free-living bacteria (like Azotobacter and Anabaena).

2. **Identifying the Role of Bacteria**:
- The bacteria involved in nitrogen fixation convert atmospheric nitrogen into ammonia. This is crucial because plants cannot directly utilize atmospheric nitrogen.

3. **Formation of Ammonia**:
- The first stable product formed during biological nitrogen fixation is ammonia (NH₃). This is the initial product that results from the conversion of atmospheric nitrogen by nitrogen-fixing bacteria.

4. **Subsequent Processes**:
- After ammonia is produced, it can undergo further oxidation to form nitrite (NO₂⁻) and then nitrate (NO₃⁻). However, these are not the first stable products of nitrogen fixation.

5. **Conclusion**:
- The first stable product of biological nitrogen fixation is ammonia (NH₃).

### Final Answer:
The first stable product of biological nitrogen fixation is **Ammonia (NH₃)**.

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