Answer:
Chargaff's rule, also known as the complementary base pairing rule, states that DNA base pairs are always adenine with thymine (A-T) and cytosine with guanine (C-G). A purine always pairs with a pyrimidine and vice versa. However, A doesn't pair with C, despite that being a purine and a pyrimidine.
Step-by-step explanation:
Complementary base pairs refer to the nitrogenous bases adenine, thymine, cytosine, and guanine. in a double strand of DNA, adenine will always pair with its complement thymine and cytosine will always pair with its complement guanine. This means that the two strands are complementary to each other. For example, a strand of DNA with a nucleotide sequence of AGTCATGA will have a complementary strand with the sequence TCAGTACT.