Question

which step shows nitrogen fixation? uptake of nitrates by plants conversion of atmospheric n₂ into ammonium conversion of nitrogen gas into nitrates conversion of nitrates to nitrogen gas

Explanation:

Nitrogen - fixation is the process of converting atmospheric nitrogen gas ($N_2$) into a more reactive form like ammonium ($NH_4^+$). This is done by nitrogen - fixing bacteria. The other options describe different steps in the nitrogen cycle such as nitrification, denitrification, and plant uptake.

Answer:

Conversion of atmospheric $N_2$ into ammonium