How are the number of protons and the number of neutrons related?

Both the number of protons and neutrons constitute or make up the nucleus of the atom and thus comprise the atomic mass of a given element. They also relatively have the same mass.

Because electrons have negligible mass, to account for the mass of the isotope, there must be 16 neutrons, 16 neutrally charged, massive, fundamental particles present in the sulfur nucleus. and thus finally, if we have the 32s2− ion, there are 18 electrons, 16 protons, and 16 neutrons.