The process that is the opposite of nitrogen fixation is

Options

A. Nitrification
B. Denitrification
C. Ammonification
D. Nitrate reduction

Answer

**Step-by-Step Solution:**

1. **Understanding Nitrogen Fixation:**
- Nitrogen fixation is the process where atmospheric nitrogen (N₂) is converted into ammonia (NH₃) by certain bacteria, including symbiotic bacteria (like Rhizobium) and free-living bacteria (like Azotobacter). This process is essential for making nitrogen available to plants in a usable form.

2. **Identifying the Opposite Process:**
- To find the opposite of nitrogen fixation, we need to look for a process that converts nitrogen compounds back into atmospheric nitrogen.

3. **Exploring the Options:**
- **Denitrification:** This is the process where nitrates (NO₃⁻) are converted back into nitrogen gas (N₂), effectively returning nitrogen to the atmosphere. This process is primarily carried out by denitrifying bacteria.
- **Nitrification:** This process involves the conversion of ammonia (NH₃) into nitrates (NO₃⁻) and is not the opposite of nitrogen fixation.
- **Ammonification:** This is the process where organic nitrogen is converted into ammonia (NH₃) and is also not the opposite of nitrogen fixation.
- **Nitrate Reduction:** This refers to the reduction of nitrates to ammonia, which does not represent the reverse of nitrogen fixation.

4. **Conclusion:**
- The process that is the opposite of nitrogen fixation is denitrification, as it converts nitrogen compounds back into atmospheric nitrogen.

**Final Answer:**
The process that is the opposite of nitrogen fixation is **denitrification**.

---