Question

The largest reservoir of nitrogen on earth is:
A. Soil
B. Oceans
C. Air
D. Granite rocks

Answer 1

Hint: The dry air we breathe predominantly consists of nitrogen gas. The percentage of nitrogen by volume in the earth’s atmosphere is approximately 78.09%, which is almost three times the percentage of oxygen.

Complete answer:
Nitrogen is a crucial element in the sustenance of basic life on earth. It is one among the major four elements (C, O, and H) that together form the basis for building biomass. Ranging from construction of complex bio-molecules like nucleic acid (DNA and RNA) and amino acids in animals to chlorophyll in plants, nitrogen play varied roles.
Nitrogen is reserved in the form of dinitrogen gas in the atmosphere, and is called atmospheric nitrogen. Oceans accommodate nitrogen in the form of triple bonded nitrogen gas as well. Soil and sediments have an organic form of nitrogen which has been accumulated in and hard to degrade over ages. When compared to these other biological and geological reservoirs, the amount of nitrogen in the atmosphere is a million fold in atmosphere. It is least found in land biota.
Living beings are not adept at utilising atmosphere nitrogen for the biological process as it is very less reactive. There exists an efficient way of fixing atmospheric nitrogen to make it available to plants in the form of nitrate, by the process of ammonia assimilation and nitrification.

So, the correct answer is C.

Note: It has been anticipated that nitrogen gas was confined in the rubble that initially coalesced to form the earth. However, with the evolution of earth as a whole, the geological components of earth (crust, mantle and core) have a reduced size of nitrogen reservoir as compared to the atmosphere.