Question

Nitrogen fixing can be done by:
(A) Industries
(B) Rhizobium
(C) Lightning
(D) All of the above

Answer 1

Hint:Nitrogen fixing is the process by which the nitrogen which is present in the atmosphere can be converted into certain compounds so that it can be used by plants and animals. There are ways by which the nitrogen can be fixed and they are industrial processes, lightning, etc. the nitrogen is to be fixed because animals and plants are not able use the direct nitrogen present in the atmosphere. Nitrogen is essential for survival of life because it is used in protein synthesis.

Complete answer:Nitrogen is also fixed by industrial process and the process is Haber process. In this process nitrogen is converted into ammonia. The raw materials required for this is air which supplies nitrogen, water and natural gas which supplies hydrogen and iron as the catalyst. Now in the process firstly the nitrogen gas from air is mixed with hydrogen gas in a ratio of 1:3. Then it is passed through the catalyst under four beds. The cooling also takes place in each pass by making the equilibrium constant. The procedure is done by maintaining the temperature around \[{{400}^{o}}-{{450}^{o}}\]and pressure of 150atm to 200atm. Then the shift conversion and carbon dioxide gas removal occurs. Then steam reforming and the methanation process occurs. Now at last the ammonia gas is cooled and collected in liquid form. The equation is \[{{N}_{2}}(g)+3{{H}_{2}}(g)\to 2N{{H}_{3}}\].
Nitrogen fixing is done by rhizobium also. It is converted into inorganic nitrogen by them. Then it is incorporated into amino acids which are then used by plants.
Nitrogen fixation is done by lightning too. In this process nitrogen and oxygen combine together in the atmosphere and form oxides of nitrogen. These gases react with rain water and form dilute nitric acid. Then these traces of nitric acid react with the mineral present in soil to form nitrates.

Hence the correct option for this answer is option (D).

Note:Nitrogen fixation is a costly process as it requires a large amount of energy. It requires around 150 calories of energy per mole of nitrogen gas fixed. It is not worthwhile for the plants to grow in nitrogen deficient habitats. Nitrogen fixing bacteria does 90% of all nitrogen fixation, thus plays an important role in the nitrogen cycle.