What is the overall process that turns ammonia into nitrates and eventually nitrogen gas?

• A. Adsorption
• B. Nitrification/denitrification
• C. Oxidation-reduction
• D. Coagulation

Answer: (B)

The process being described is a two-step biological nitrogen removal: nitrification followed by denitrification. In aerated conditions, ammonia is oxidized first to nitrite and then to nitrate by specialized bacteria—this is nitrification. Then, in low-oxygen (anoxic) conditions, denitrifying bacteria use nitrate as an electron acceptor and convert it to nitrogen gas, which escapes to the atmosphere. Together, these steps turn ammonia into nitrates and eventually into nitrogen gas. Other options don’t describe this biological sequence: adsorption just traps impurities, oxidation-reduction is a broad redox idea not the specific two-step pathway, and coagulation is a particles-removal process.