When ammonia is converted into nitrites and nitrates called nitrification. It is biological process in which nitrites and nitratesare reduced to nitrogen gas by denitrifying bacteria. By the process, nitrogen is returned to atmosphere called denitrification. Correct Answer When ammonia is converted into nitrites and nitrates called nitrification. It is biological process in which nitrites and nitratesare reduced to nitrogen gas by denitrifying bacteria. By the process, nitrogen is returned to atmosphere called denitrification.