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 analyze the role of nitrogenase enzymes in various nitrogen-related processes and determine which process will not occur if these enzymes are inactivated.

### Step-by-Step Solution:

1. **Understanding Nitrogenase Enzymes**:
- Nitrogenase is an enzyme crucial for the biological fixation of atmospheric nitrogen (N2) into ammonia (NH3). This process is primarily carried out by certain bacteria, including those associated with the roots of legumes.

2. **Analyzing Each Statement**:
- **Statement (i)**: Fixation of atmospheric `NO2`.
- Nitrogenase is not involved in the fixation of nitrogen oxides like NO2. Other mechanisms can facilitate this process. Therefore, this statement can still occur.

- **Statement (ii)**: Conversion from nitrate to nitrite in legumes.
- This process is mediated by the enzyme nitrate reductase, not nitrogenase. Thus, the inactivation of nitrogenase does not affect this conversion. This statement can still occur.

- **Statement (iii)**: Fixation of nitrogen in legumes.
- This process directly depends on nitrogenase. If nitrogenase is inactivated, nitrogen fixation in legumes will not occur. This statement will not occur.

- **Statement (iv)**: Conversion from ammonium to nitrate in soil.
- This conversion is carried out by the enzyme ammonium monooxygenase, which is independent of nitrogenase. Therefore, this statement can still occur.

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

Thus, the final answer is:
**(iii) Fixation of nitrogen in legumes will not occur.**