Question

The process of biological nitrogen-fixation does not take place in the presence of:
(a) molecular form of hydrogen
(b) elemental form of oxygen
(c) elemental form of nitrogen

Answer 1

(b) elemental form of oxygen

Certain bacteria such as Azotobacter (occur freely in the soil) and Rhizobium (occur in root nodules of leguminous plants), convert the atmospheric nitrogen into water-soluble nitrates and nitrites. The process of biological fixation of nitrogen is called as nitrogen fixation.
Enzymes required for nitrogen fixation are nitrogenases. These nitrogenases are very susceptible to destruction by oxygen. Many bacteria cease the production of enzymes in the presence of oxygen. Many nitrogen-fixing bacteria grow in anaerobic conditions or respire to bring down oxygen levels.