What did Rosalind Franklin contribute to understanding DNA?

• A. Proved DNA is the genetic material
• B. DNA is a single strand
• C. DNA is composed of sugars and phosphates
• D. Confirmed the double helix shape of DNA with X-ray diffraction photos

Answer: (D)

The main idea here is recognizing how Franklin’s use of X-ray diffraction revealed the shape of DNA. She used X-ray crystallography on DNA fibers and produced high-quality images that showed an X-shaped pattern, which is a hallmark of a helical structure. The pattern and the spacing observed in her data pointed to a regular, two-stranded, helical molecule with a consistent diameter and repeating base-pair structure. This real evidence about the geometry of DNA helped scientists infer that DNA is a double helix, a key step toward the correct model.

That’s why this answer is the best: Franklin’s diffraction images provided direct, visual evidence about DNA’s form, rather than just its chemical components or its identity as genetic material. The other options describe important ideas in genetics and chemistry, but they aren’t what Franklin’s diffraction work showed.