How many atoms are present in 34.96 moles of mg

Multiply amount in grams by the relative atomic mass of magnesium then multiply by avagodro constant (6.02*10^23)

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.

You would do 1500/4 and the answer is 375