15. Which species contains 16 protons, 17 neutrons and 18 electrons?
a. 325
b. 3382-
d. 3592-
C. 345

Thus, each atom or ion of sulfur must contain 16 protons. We are told that the ion also has 16 neutrons, meaning the mass number of the ion is 16 + 16 = 32. Because the ion has 16 protons and 18 electrons, its net charge is 2–. Thus, the symbol for the ion is 32S2–.