Which one of the following is a nitrogen fixing enzyme?

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Which one of the following is a nitrogen fixing enzyme? Answer: None of these

The enzyme responsible for nitrogen fixation is nitrogenase, not nitrate reductase, urease, or arginase. Nitrogenase converts atmospheric nitrogen (N₂) into ammonia (NH₃) in symbiotic bacteria like Rhizobium, which is crucial for plant nitrogen supply.