Question

The X-ray diffraction photography of Rosalind Franklin and Maurice Wilkins was critical evidence of DNA
(a) Indicating that DNA has a double helix structure
(b) Showing equal numbers of purines and pyrimidines
(c) Showing the bases of DNA were held together by hydrogen bonds
(d) Revealing the structure of the deoxyribose sugar

Answer 1

Hint: X-ray diffraction photography is one of the imaging methods used in medical science. In this method, X-ray is used to detect the structure and molecular arrangement of the object on which it falls by the process of diffraction. This process is also called crystallography as it helps in detecting 3-D structure of crystals.

Complete answer
X-ray diffraction photography method was invented by Rosalind Franklin and Maurice Wilkins. This method helped in detecting structures of many microscopic objects.
This was the method that helped sir Watson and Crick to detect the structure that is, the double helical model of DNA. Therefore, we can say that X-ray diffraction photography helped in indicating that DNA has a double helix structure. So, option A is the correct answer.
X-ray diffraction photography is concerned with only structure detection and not chemical arrangement of the object. Therefore, the method can never determine the presence of equal numbers of purine and pyrimidine in the double helical structure of DNA. So, option B is an incorrect option.
Since, the X-ray diffraction photography determines the structure of a crystal with the help of interferences introduced by its surface through diffraction of X-ray, so it is impossible for it to detect the kind of bond between the molecules. Thus, option C is also an incorrect option.
The imaging method is capable of giving only a broad idea of structure or molecular arrangement of the crystal. Pentose sugar is one of the components of the double helical DNA, so is quite difficult to be detected by X-ray diffraction photography. Thus, option D is also an incorrect option.

So the correct answer is option a) Indicating that DNA has a double helix structure.

Note:
However, whenever questions also about the discoverers of the double helical model of DNA then the answer will be Watson and Crick only because they were the first one to determine the structure of DNA by using the X-ray diffraction photography method.