The process of `N_(2)` fixation in root nodules is controlled by

Options

A. nif
B. NAA
C. IAA
D. ABA

Answer

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into a form that plants can use, such as ammonium ions (NH₄⁺). This process is crucial for plant growth as nitrogen is an essential nutrient.

2. **Role of Root Nodules**:
- In many plants, particularly legumes, nitrogen fixation occurs in specialized structures called root nodules. These nodules are formed in symbiosis with nitrogen-fixing bacteria, primarily from the genus Rhizobium.

3. **Key Genes Involved**:
- The process of nitrogen fixation is controlled by specific genes. The two main types of genes involved are:
- **NIF Genes**: These genes encode for the nitrogenase enzyme, which is essential for the conversion of atmospheric nitrogen into ammonium ions.
- **Nod Genes**: These genes are responsible for the production of nod factors, which stimulate the formation of root nodules in the host plant.

4. **Identifying the Correct Answer**:
- Among the options provided (F and AA, IAA and AB), the correct answer is related to the NIF genes, as they directly control the nitrogen fixation process in root nodules.

5. **Eliminating Incorrect Options**:
- The other options mentioned (NAA, IAA, and AB) refer to plant hormones that are not directly involved in the nitrogen fixation process.
- NAA (Naphthaleneacetic acid) is a synthetic auxin.
- IAA (Indole-3-acetic acid) is a natural auxin involved in plant growth.
- AB (Abscisic acid) is a stress hormone.

6. **Conclusion**:
- Therefore, the process of nitrogen fixation in root nodules is primarily controlled by the **NIF genes**.