Assertion: The enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric nitrogen to ammonia.
Reason: The enzyme nitrogenase is highly sensitive to the molecular oxygen.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. if both assertion and reason are true but reason is not the correct explanation of assertion
C. if assertion is true but reason is false
D. if both assertion and reason are false

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that nitrogenase is a Mo-Fe protein that catalyzes the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃). This is a true statement, as nitrogenase is indeed composed of molybdenum (Mo) and iron (Fe) and plays a crucial role in nitrogen fixation.

2. **Understanding the Reason**: The reason provided states that nitrogenase is highly sensitive to molecular oxygen (O₂). This statement is also true. Nitrogenase requires an anaerobic environment to function effectively, as the presence of oxygen can inhibit its activity.

3. **Analyzing the Relationship**: We need to determine if the reason provided explains the assertion. While both statements are true, the sensitivity of nitrogenase to oxygen does not directly explain its function of converting atmospheric nitrogen to ammonia. The assertion describes what nitrogenase does, while the reason describes a condition necessary for its activity but does not explain the mechanism of nitrogen fixation.

4. **Conclusion**: Since both the assertion and reason are true, but the reason does not serve as a correct explanation for the assertion, we conclude that the answer is: Both assertion and reason are true, but the reason is not the correct explanation of the assertion.

### Final Answer:
Both assertion and reason are true, but reason is not the correct explanation of assertion.

---