Final answer:
Adenine (A) and thymine (T) form two hydrogen bonds, while cytosine (C) and guanine (G) form three hydrogen bonds in DNA.
Step-by-step explanation:
The number of hydrogen bonds that exist between the base pairs in DNA is crucial for the stability of the DNA double helix structure. Adenine (A) and thymine (T) are complementary bases that form exactly two hydrogen bonds between them, ensuring a consistent distance between the two DNA strands. In contrast, cytosine (C) and guanine (G) pair together with three hydrogen bonds. This difference in the number of hydrogen bonds contributes to the characteristic shape and stability of the DNA molecule.