How many grams are in 0.02 moles of beryllium iodide, bel2?

This set up of a conversion table should show you that if you multiply the grams of BeI2 times .02 moles, it equals 5.256 g (your answer) 

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.