If by radiation all the nitrogenase enzymes are inactivated , then Which of the following will not occur ?
(i) Fixation of atmospheric `NO_2`
(ii) Conversion from nitrate to nitrite in legumes
(iii) Fixation of nitrogen in legumes
(iv) Conversion from ammonium to nitrate in soil

Options

A. (ii) and (iii)
B. (i) and (iii)
C. (ii) and (iv)
D. (iii) only

Answer

To solve the question, we need to understand the role of nitrogenase enzymes and the processes mentioned in the options.

### Step-by-Step Solution:

1. **Understanding Nitrogenase Enzymes**:
- Nitrogenase is an enzyme responsible for the fixation of atmospheric nitrogen (N₂) into a form that plants can use, such as ammonia (NH₃). This process is crucial for the nitrogen cycle and is primarily carried out by certain bacteria, including those found in the root nodules of leguminous plants.

2. **Analyzing Each Option**:
- **Option (i)**: Fixation of atmospheric NO₂ (Nitrogen Dioxide).
- This option is incorrect because nitrogenase does not fix NO₂; it fixes N₂. Therefore, this process is not directly related to nitrogenase activity.

- **Option (ii)**: Conversion from nitrate to nitrite in legumes.
- This process is typically carried out by other enzymes (nitrate reductase) and does not involve nitrogenase. Thus, this option is also not directly affected by the inactivation of nitrogenase.

- **Option (iii)**: Fixation of nitrogen in legumes.
- This process directly involves nitrogenase. If nitrogenase is inactivated, nitrogen fixation in legumes will not occur. Therefore, this option is a direct consequence of nitrogenase inactivation.

- **Option (iv)**: Conversion from ammonium to nitrate in soil.
- This process is known as nitrification and is carried out by different bacteria, not nitrogenase. Therefore, this option is also not affected by the inactivation of nitrogenase.

3. **Conclusion**:
- The only process that will not occur if nitrogenase enzymes are inactivated is the **fixation of nitrogen in legumes** (Option iii).

Thus, the correct answer is **(iii) Fixation of nitrogen in legumes**.