“Denitrifying” bacteria return molecular nitrogen gas (N2) back into the biosystem by a series of reductions. Identify the correct sequence. Select the correct answer below: A. NO−3→NO−2→N2O→N2 B. N2O→NO−3→NO−2→N2 C. N2O→NO−2→NO−3→N2 D. NO−3→N2O→NO−2→N2

NO−3→NO−2→N2O→N2

Explanation:

Denitrification is the process by which nitrogen is returned to the atmosphere by denitrifying bacteria. The process of denitrification involves a sequence of reduction reactions in the sequence; NO3−→NO2−→N2O→N2.

Nitrogen is usually present in soil in the form of soil nitrates which are soluble in water and can be absorbed by plant roots. These denitrifying bacteria reduce soil nitrates to nitrites, then to nitrogen I oxide and finally to molecular nitrogen as shown in the sequence above.

Denitrification can release N2O, is an ozone-depleting substance and

greenhouse gas into the atmosphere with its attendant consequence on global warming.