Question

which process in the nitrogen cycle takes extra nitrogen from the soil and puts it back into the air?
a. denitrification
b. assimilation
c. fixation
d. eutrophication

Explanation:

Denitrification is the process where bacteria convert soil nitrates back to atmospheric nitrogen ($N_2$). Assimilation is when organisms take up nitrogen; fixation converts atmospheric $N_2$ to soil nitrogen; eutrophication is nutrient over-enrichment (not a nitrogen cycle process). The question asks for returning soil nitrogen to air, which matches denitrification.

Answer:

A. Denitrification