Final answer:
Rosalind Franklin used x-ray diffraction to reveal the structure of DNA, and her critical work led to the discovery of its double helix structure.
Step-by-step explanation:
The scientist who used x-ray diffraction to help reveal the geometric structure of DNA was Rosalind Franklin. Although James Watson and Francis Crick are often credited with the discovery of the double helix structure of DNA, it was Franklin's critical X-ray diffraction pattern of DNA that elucidated its double helix structure. Watson and Crick used Franklin's data as a key piece of the puzzle in formulating the structural model of DNA. Regrettably, Franklin's contribution was not officially recognized by the Nobel Committee as she passed away before the Nobel Prize in Physiology or Medicine was awarded to Watson, Crick, and Maurice Wilkins in 1962.