Final answer:
Adenine forms two hydrogen bonds with thymine, and guanine forms three hydrogen bonds with cytosine; adenine does not pair with guanine in DNA.
Step-by-step explanation:
The student asks how many hydrogen bonds exist between adenine and guanine within a base pair. The correct answer is that adenine (A) does not directly bond with guanine (G) in a stable base pairing. Adenine forms two hydrogen bonds with thymine (T), while guanine forms three hydrogen bonds with cytosine (C) in the DNA double helix structure. In the context of DNA, complementary base pairs are always formed between adenine and thymine (A-T) and between guanine and cytosine (G-C). This complementarity ensures the stability of the DNA structure, maintaining the uniform shape of the DNA double helix.