Free nitrogen refers to atmospheric nitrogen (N₂) that is abundant in the Earth's atmosphere but is in a form that plants and most organisms cannot use directly. Therefore, the correct answer is:
nitrogen that cannot be used by organisms
For plants to utilize nitrogen, it must be fixed into forms such as ammonium (NH₄⁺) or nitrate (NO₃⁻), which is achieved by certain bacteria and processes in the nitrogen cycle.
1 answer