Which one of the following mineral elements plays an important role...

Molybdenum is a micronutrient specifically for plants that form root nodules with nitrogenfixing bacteria, though plants that do not form nodules also use trace amounts of it in a protein involved with nitrogen metabolism and uptake. Related Theory The main functions of leghaemoglobin are (1) to facilitate oxygen supply to the nitrogen fixing bacteria and (2) to protect the enzyme, nitrogenase from being inactivated by oxygen.