Who are credited with discovering the DNA double helix?

• A. Amino acid
• B. Nitrogen base
• C. Watson and Crick
• D. 5-carbon sugar

Answer: (C)

The main idea here is recognizing who first proposed the accurate three-dimensional model of DNA. Watson and Crick are credited because they built and published the first correct model of DNA in 1953, showing two strands twisted into a right-handed double helix with a sugar–phosphate backbone on the outside and base pairs on the inside. This arrangement fits Chargaff’s rules, which show A pairs with T and G pairs with C, and it explains how genetic information could be copied, since each strand can serve as a template for the other during replication. They also drew on X-ray diffraction data that indicated a helical shape, helping to constrain the model. The other options refer to components of DNA (like the nitrogen bases or sugar) rather than people who proposed the structure, so they don’t answer who discovered the double helix.