The information that can be determined directly from the X ray diffraction photographs of crystallized DNA is the diameter of the DNA helix, thus, the correct option is A.
The technique that is used in this way to determine the structure of DNA is called X ray crystallography. X ray crystallography involves the exposure of pure crystals of DNA to X ray in order to determine the location of its molecules. The method was first used by Rosalind Franklin to elucidate the structural properties of DNA. The work of Watson and Crick, who discovered the helical structure of DNA was based on the research findings of Rosalind Franklin.
