This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fundamentals In Radiology, Subject name: Radiology
[{'content': 'Substances with same atomic number but different mass number are \nSelect and explain. \nA. Isotopes, B. Isobars, C. Isomers, D. Any of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a (Isotope) (Ref. Radioactive isotope in Medicine Biology by Quimby, 2nd ed., 26)TermDefinitionisotopesAtoms having same:- atomic number (same number of protons),- position in periodic table, and- chemical and metabolic properties, but diffeient;- number of neutrons,- mass number (protons plus neutrons),- density and other physical properties. E.g., 17CI-35, 17CI-37.IsobarsAtoms having same mass numbers, different atomic number (hence different neutron number) e.g., 28Ni-64, 30Zn-64IsotonesAtoms having same neutron number, different atomic mass number, e.g., 18A-40IsomersAtoms having same atomic and mass numbers but different energy states in nucleus', 'role': 'assistant'}]