1. Dinitrogen gas (N2):

- Dinitrogen gas is the most abundant form of nitrogen in the atmosphere, accounting for approximately 78%.

- However, humans cannot directly metabolize N2 and must rely on microorganisms, such as nitrogen-fixing bacteria, to convert it into usable forms of nitrogen.

2. Nitrous oxide (N2O):

- Nitrous oxide, also known as laughing gas, is an intermediate product of denitrification and nitrification processes.

- Although it is released from the ground as a result of both natural and human-induced activities, the form is unsuitable for direct human assimilation or incorporation into plant tissues.

3. Nitrogen oxides (NOx):

- Nitrogen oxides refer to a group of molecules, including nitric oxide (NO), nitrogen dioxide (NO2), and dinitrogen tetroxide (N2O4).

- While released during combustion processes and involved in atmospheric reactions, they are largely unavailable for direct human utilization.