Correct option is C
✅ (c) Nitrogen fixation: • Nitrogenase is a key enzyme that converts atmospheric N₂ into ammonia (NH₃), a usable form for plants. • Found in Rhizobium (legume nodules) and Azotobacter (free-living). • Requires anaerobic conditions and energy (ATP) to function.
❌ (a), (b), (d): • These are part of nitrogen metabolism but are not catalyzed by nitrogenase.