In this question, we have to find the number of atoms in 12.5 moles of Sulfur, and the way to do it is by using the Avogadro's number, which is 6.02*10^23 atoms, this value represents how many atoms we have in 1 single mol of any element. Therefore in 12.5 moles we will have:
1 mol = 6.02*10^23 atoms
12.5 moles = x atoms
x = 7.52*10^24 atoms of Sulfur in 12.5 moles
