Final answer:
AT is less stable than GC pairs due to fewer hydrogen bonds and the strength of the bonds. Repulsive interactions at short internuclear distances also contribute to the lower stability of AT pairs.
Step-by-step explanation:
AT is less stable than GC pairs because AT pairs have fewer hydrogen bonds compared to GC pairs. Hydrogen bonds are important for stabilizing the DNA double helix structure and holding the base pairs together. GC pairs have three hydrogen bonds, while AT pairs have only two hydrogen bonds. This difference in hydrogen bonding makes GC pairs more stable and less likely to break.
Additionally, the stability of a molecule is influenced by the strength of its bonds. The stronger the bonds, the more stable the molecule. GC pairs have stronger hydrogen bonds than AT pairs, which makes them more stable.
In terms of internuclear distance, at very short distances, repulsive interactions dominate and make the system less stable than the isolated atoms. This can also contribute to the higher likelihood of AT pairs breaking.