Which of the following micronutrients is known to aid in nitrogen fixation in legumes?

Molybdenum plays a crucial role in nitrogen fixation, especially in legumes. It acts as a cofactor for the enzyme nitrogenase, which is essential for converting atmospheric nitrogen (N2) into a form that plants can utilize, such as ammonia (NH3). This process is vital for legumes, which have a symbiotic relationship with nitrogen-fixing bacteria, particularly Rhizobium, in their root nodules. Molybdenum deficiency can lead to impaired nitrogen fixation, reducing the availability of nitrogen needed for the growth and development of the legume plants.

The other micronutrients listed, such as boron, iron, and manganese, are important for various plant functions, but they do not specifically aid in the process of nitrogen fixation in the same way that molybdenum does. For example, boron is primarily involved in cell wall formation and reproductive growth, iron is essential for chlorophyll synthesis and enzyme functions, and manganese plays a role in photosynthesis and respiratory processes. Thus, while these micronutrients are essential for plant health, molybdenum's specific function in nitrogen fixation sets it apart as the correct answer in this context.