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.

Answer 2

The answer is phosphorus-32.

We know that the atom contains 15 protons, 15 electrons, and 17 neutrons.
To conclude of which element this radionuclide is, we need to know an atomic number of the element. The atomic number of the element is the number of proton in the nucleus of the atom. If the number of protons is 15, then the atomic number is 15. The element with atomic number 15 is phosphorus (according to the periodic table).
To conclude which phosphorus isotope this radionuclide is we need to know the mass number of the element. The mass number of the element is the sum of the number of protons and number of neutrons in the nucleus of the atom. If the number of protons is 15 and the number of neutrons is 17, then the mass number is 17 + 15 = 32.
Thus, this radionuclide is phosphorus-32.