3. In order to solve this one, we will use Avogadro's number, which is a constant that represents the value for 1 mol, this number is equal to 6.02*10^23 atoms, molecules or formula units
1 mol = 6.02*10^23
3.96 moles = x formula units
x = 2.38*10^24 formula units
Letter A
4. The reaction Zn + CuSO4 -> ZnSO4 + Cu, can also be read as Zinc, in the elemental form, since there is no bond with any other element; Copper (II) sulfate, since sulfate has a 2- charge, Copper must have a 2+ charge to compensate; Zinc sulfate and copper in the elemental form, so the final read will be
Zinc and Copper (II) sulfate yields Zinc sulfate and copper
Letter B