Final answer:
Erwin Chargaff is the biochemist who discovered the proportional concentrations of adenine to thymine and guanine to cytosine, which are known as Chargaff's rules. Therefore, the correct answer is D) Erwin Chargaff.
Step-by-step explanation:
The individual who noticed the concentration of adenine (A) and thymine (T) was proportional, as well as guanine (G) and cytosine (C), implying that A and T, and G and C might be pairing, was Austrian biochemist Erwin Chargaff. This discovery, which showed that (A+G) = (T+C) and set the stage for the identification of the double-helix structure of DNA, is known as Chargaff's rules.
Chargaff's findings were critical for James Watson and Francis Crick when they proposed the DNA double helix model. He found, through quantitative analysis, that the amount of A is always equal to T, and the amount of G is always equal to C, despite variances in DNA composition across different species. These pairings are known as complementary bases.