- A Nitrogen gas released back into the atmosphere
- B Ammonia or nitrates usable by plants
- C Nitrogen dioxide formed during combustion
- D Pure nitrogen metal deposited in soil
Correct answer: B. Ammonia or nitrates usable by plants
Explanation: Nitrogen fixation converts N2 gas (inert) into ammonia (NH3) or nitrates that plants can absorb. Without this process, atmospheric N2 is unavailable to most organisms.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.