DNA molecule has two strands in which the four complementary bases pair to each other, i.e. cytosine (C) pairs with guanine (G), while thymine (T) always pairs with adenine (A). When DNA molecule is hydrolysed, the molar mass of cytosine is always equal to that of guanine and adenine equal to thymine.
In RNA, there is no relationship between the quantities of four bases (C, G, A and U) obtained, i.e. the base pairing principle is not followed.
That is why, unlike DNA, RNA is single stranded