Which of the four most abundant element in most plants (C, H, O and N), dows a terrestrial green plant procure mainly through its roots from the soil?

Answer: BSolution: Hydrogen (H) is mainly obtained from soil water by roots. Oxygen (O) is either derived from the wair or from the water. Carbon (C) is derived from atmosphere as $C{O}_2$. The plants are unable to use atmospheric nitrogen. It is inert and plants cannot make use of it directly. By the process of fixation of atmospheric $N_2$ nitrates $\left(N{O}_3^{-}\right)$, ammonium ion $\left(N{H}_4^{+}\right)$, etc. These nitrogenous compounds enter plants as nutrietns through the roots and are assimilated as organic nitrogen.