Final answer:
Guanine (G) forms three hydrogen bonds with cytosine (C) in DNA, providing stability to the structure of the DNA molecule through specific geometrical pairing.
Step-by-step explanation:
The answer to the question "Guanine to cytosine has how many H-bonds?" is that guanine (G) forms three hydrogen bonds with cytosine (C). In a DNA molecule, the nitrogenous bases pair up between two strands, with adenine pairing with thymine (A-T) by two hydrogen bonds, and guanine with cytosine (G-C) by three hydrogen bonds. This pairing is due to the specific geometries of the base molecules, which allows for maximum hydrogen bonding and the stability of the DNA structure. The base pairs are held together within the DNA's double helix by these hydrogen bonds, which are crucial for the DNA's structure and function.