Final answer:
The base pair with poor stacking is Adenine-Guanine (A-G) as it does not follow the proper base pairing rules of DNA, where adenine is meant to pair with thymine and guanine is meant to pair with cytosine.
Step-by-step explanation:
The base pair that has bad stacking is Option C, Adenine-Guanine (A-G). In DNA, the correct base pairing occurs between a purine and a pyrimidine; specifically, adenine pairs with thymine and guanine pairs with cytosine. This pairing is due to their structural compatibility and the ability to form hydrogen bonds—adenine and thymine form two hydrogen bonds, and cytosine and guanine form three. Base pairing follows Chargaff's rules, where the amount of adenine always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine. Thus, adenine pairing with guanine would be incorrect as they are both purines and cannot form the necessary hydrogen bonds nor maintain the DNA helix's structural integrity.
The base pairs in DNA are formed by complementary pairing between purines and pyrimidines. Adenine (A) always pairs with Thymine (T), while Guanine (G) always pairs with Cytosine (C). Therefore, option B) Guanine-Cytosine (G-C) is the correct answer as it represents a base pair with good stacking.