Which base pair is easier to denature due to having fewer hydrogen bonds?

The base pair that is easier to denature due to having fewer hydrogen bonds is adenine and thymine. This particular pairing forms two hydrogen bonds, while the other combinations typically form three hydrogen bonds. The stability of DNA is partly determined by the number of hydrogen bonds between the base pairs; the more hydrogen bonds present, the more energy is required to separate the strands.

In contrast, other pairs, like guanine and cytosine, form three hydrogen bonds. This additional bond creates a stronger interaction, making them more stable and harder to denature. Adenine and cytosine, as well as cytosine and thymine, also have differing numbers of hydrogen bonds, but adenine and thymine's two bonds make it the least stable of the options provided, leading to easier denaturation under conditions such as heat or changes in pH.

Therefore, the adenine-thymine pair is less stable than others due to its lower number of hydrogen bonds, making it easier to denature.