Question

A radioactive nuclide is used to detect eye tumors. An atom of this radionuclide contains 15 protons, 15 electrons, and 17 neutrons. Which is symbol of this radionuclide?

Answer 1

Knowing that the number of protons of an element is equivalent to its atomic number, it can be determined from the periodic table of elements that this radionuclide is phosphorus. Since the number of its neutrons is 17, it can also be determined that its atomic mass is n + p = 15 + 17 = 32. This means the isotope is phosphorus-32.