Answer:
The correct answer would be the first option.
Nitrogen cycle refers to the cyclic movement of nitrogen in which it travels through different spheres in nature.
Different processes involves in a nitrogen cycle are: nitrogen fixation, ammonification, nitrification, and denitrification.
Nitrogen fixation refers to the process by which atmospheric nitrogen is converted into compounds that can be used by plants. It is achieved by three means: atmospheric processes (such as thundering), industrial, and biological processes.
Biological nitrogen fixation refers to the type of nitrogen fixation in which atmospheric nitrogen is converted into nitrates or nitrites through nitrogen-fixing microorganisms.
For example, <em>Rhizobium </em>(symbiotic nitrogen-fixing bacteria), <em>Azotobacter </em>(free-living nitrogen-fixing bacteria, et cetera.
