Given below are two statements: Statement I: A unit formed by the attachment of a base to the 1' position of sugar is known as a nucleoside. Statement II: When a nucleoside is linked to phosphorous acid at the 5'-position of the sugar moiety, we get a nucleotide. In the light of the above statements, choose the correct answer from the options given below:

Solution & Explanation

\textbf{Answer:} (C) Statement I is true, but a nucleotide forms with phosphoric acid (not phosphorous acid), so Statement II is false. \textbf{Solution:} Statement I is correct: attaching a nitrogenous base to the 1' position of the pentose sugar gives a nucleoside. Statement II is wrong: a nucleotide is formed when the nucleoside is esterified at the 5'-position with phosphoric acid $\mathrm{H}{}_3\mathrm{PO}{}_4$, not phosphorous acid $\mathrm{H}{}_3\mathrm{PO}{}_3$. Hence Statement I is true but Statement II is false, giving option C.