A DNA molecule has two strands in which the four complementary bases pair each other, i.e., cytosine \((\mathrm{C})\) always pair with guanine \((\mathrm{G})\) while thymine ( \(\mathrm{T})\) always pairs with adenine (A). Thus, when a DNA molecule is hydrolysed, the molar amounts of cytosine is always equal to that of guanine and that of adenine is always equal to thymine.
In RNA, there is no relationship between the quantities of four bases ( \(\mathrm{C}, \mathrm{G}, \mathrm{A}\) and \(\mathrm{U})\) obtained, therefore, the base pairing principle, i.e. A pairs with \(U\) and \(C\) pairs with \(G\) is not followed. Therefore, unlike DNA, RNA has a single strand.