Nitrogen fixation is facilitated by

Options

A. Cu
B. B
C. Zn
D. Mo

Answer

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into ammonia (NH₃), which plants can utilize. Atmospheric nitrogen is not directly usable by plants.

2. **Role of Prokaryotes**:
- Certain prokaryotes, such as the bacteria Rhizobium, are responsible for nitrogen fixation. They form symbiotic relationships with leguminous plants to facilitate this process.

3. **Enzyme Involved**:
- The key enzyme that catalyzes the conversion of atmospheric nitrogen to ammonia is called nitrogenase. This enzyme is crucial for the nitrogen fixation process.

4. **Components of Nitrogenase**:
- Nitrogenase is a molybdenum-iron protein. Molybdenum (Mo) and iron (Fe) are essential components of this enzyme, enabling it to function effectively in the conversion process.

5. **Sensitivity to Oxygen**:
- Nitrogenase is highly sensitive to molecular oxygen (O₂). To protect the enzyme from oxygen, a pigment called leghemoglobin is present in the root nodules of leguminous plants. Leghemoglobin acts as an oxygen scavenger, maintaining an anaerobic environment necessary for nitrogenase activity.

6. **Conclusion**:
- Given that molybdenum is a critical component of the nitrogenase enzyme, it plays a significant role in facilitating nitrogen fixation. Therefore, the correct answer to the question is that nitrogen fixation is facilitated by **molybdenum**.