What term describes the two nucleotides on complementary strands of DNA that form a pair?

The term that describes the two nucleotides on complementary strands of DNA that form a pair is "base pair." In DNA, the structure is formed by two strands that run in opposite directions, with each nucleotide on one strand pairing with a complementary nucleotide on the other strand. These pairs consist of specific combinations of bases: adenine pairs with thymine, and guanine pairs with cytosine. The stability and structure of the DNA double helix are largely due to these base pairs, which create the rungs of the helical ladder.

The other options do not accurately reflect this concept. A "gene pair" typically refers to a pair of alleles for a specific gene, while "nucleotide pair" is not a standard term used in genetics, and "chromatid pair" refers to the two sister chromatids formed during cell division. Thus, "base pair" is the precise terminology for the complementary nucleotides that bond together in the structure of DNA.