Explain the following terms
(i) Nitrogen fixation
(ii) Nitrification
(iii) Denitrification

Explanation

The process in which atmospheric nitorgen is converted into usable forms like ammonia. Nitrate or `NO_(2)` etc is called nitrogen fixation.
The processs of formation of nitriters and then to nitraters from ammonium compounds is called nitrification.
(iii) The process of conversion of some ammonium compounds, nitrites and nitrates into molecular nitrogen is called denitrification.