A DNA is a double-stranded molecule(two polynucleotide chains whose nitrogenous bases are connected by hydrogen bonds).

In this molecule pairing or connection of bases occurs. Adenine always pairs with thymine, while cytosine always pairs with guanine.

So when DNA is hydrolyzed the amount of adenine produced is exactly equal to the amount of thymine produced, similarly, the amount of cytosine produced is equal to that of guanine.

But as given when RNA is hydrolyzed, there is no relationship between the quantities of different bases obtained. This suggests that RNA is a single-stranded molecule.