Final answer:
Option (B), The statement is false; adenine and guanine are purines with a double ring structure, while cytosine and thymine are pyrimidines with a single ring structure.
Step-by-step explanation:
Understanding Nitrogenous Bases
The statement given is false. In the classification of nitrogenous bases, adenine (A) and guanine (G) are purines, which are characterized by a double carbon-nitrogen ring structure. On the other hand, cytosine (C) and thymine (T) are categorized as pyrimidines, which have a single carbon-nitrogen ring structure.
The purines and pyrimidines pair up to form base pairs in the DNA double helix, with adenine pairing with thymine, and cytosine pairing with guanine. These pairings are held together by hydrogen bonds and are essential for the structure of DNA and its function in heredity.