Q. Which two distinct microbial processes are responsible for the release of fixed nitrogen as dinitrogen gas (N2) to the atmosphere?

1. Aerobic nitrate oxidation, and nitrite reduction
2. Anaerobic ammonium oxidation, and denitrification
3. Decomposition of organic nitrogen, and conversion of dinitrogen to ammoniumcompounds
4. Enteric fermentation in cattle, and nitrogen fixation by Rhizobium in root nodules oflegumes