Answer: (2) (ii) and (iii)
Nitrogen is an essential nutrient for plant growth, development, and reproduction. The biological method occurs in the atmosphere due to UV radiations and lightening that converts dinitrogen into nitric oxide, which is further oxidized to nitrogen dioxide. These oxides dissolve in rainwater and reach soil as nitrous and nitric acid. These acids react with alkali radicals of soil and form nitrates. Plants directly absorb the soluble nitrates.
- The biological method involves converting dinitrogen into nitrogenous compounds by prokaryotes and is known as biological nitrogen fixation.
- Nitrogen assimilation is a process of absorbing nitrates and ammonia to produce organic nitrogen.