<prompt> Which technique is used to study structure of molecules -X-ray crystallographyIon exchange chromatographyElectron microscopyAgarose gel electrophoresis  <response>: In the question, they have not mentioned about the nature of structure such as 1o, 2o or 3o etc. In this case, consider teiary structure 3D structure. So, mark X-ray crystallography X-ray crystallography can detect 3-D structure of any macromolecule. ADDITIONAL INFORMATION ON THIS TOPIC Mass spectrometry: Best technique to determine-primary structure of proteins This technique is Qualitative as well as Quantitative Can detect post-translational modifications like hydroxylation or covalent modifications of enzymes like phosphorylation and dephosphorylation Can detect the exact molecular weight of the protein as the name says - MASS. 