Name the element that plays an important role in biological nitrogen fixation :

Options

A. Molybdenum
B. Manganese
C. Copper
D. Zinc

Answer

### Step-by-Step Solution:

1. **Understanding Biological Nitrogen Fixation**: Biological nitrogen fixation is the process by which certain microorganisms convert atmospheric nitrogen (N₂) into ammonia (NH₃), which can then be used by plants.

2. **Identifying Key Elements**: In this process, several elements play crucial roles, but one element is particularly significant as a cofactor in the enzymes involved in nitrogen fixation.

3. **Recognizing the Role of Molybdenum**: Molybdenum is a micronutrient that is essential for the activity of nitrogenase, the enzyme responsible for nitrogen fixation. It helps in the conversion of atmospheric nitrogen into ammonia.

4. **Absorption of Molybdenum**: Plants absorb molybdenum in the form of molybdenum ions (MoO₄²⁻). This absorption is crucial for the proper functioning of nitrogen-fixing bacteria associated with plant roots.

5. **Conclusion**: Therefore, the element that plays an important role in biological nitrogen fixation is **Molybdenum**.