The end-product of denitrification is?

• A. Nitrogen gas
• B. Oxygen gas
• C. Nitrous oxide
• D. Ammonia

Answer: (A)

Denitrification is the process where nitrate is used as the electron acceptor under anaerobic conditions, typically with organic carbon providing the energy. Denitrifying bacteria progressively reduce nitrate to nitrite, then to nitrous oxide, and finally to nitrogen gas. The nitrogen gas (N2) is the form that escapes from the water to the atmosphere, which is why this step effectively removes nitrogen from the wastewater.

Oxygen gas isn’t produced in this pathway because denitrification uses nitrate rather than oxygen as the electron acceptor. Nitrous oxide can appear as an intermediate or byproduct in some routes, but it is not the stable end product when the process runs to completion. Ammonia is related to a different nitrogen process (ammonification), not denitrification, so it isn’t the product of this pathway.