Question: how many moles of cl atoms are present?
Answer: The number of moles of Cl is twice as much, because the ratio of Cl in MgCl2 to MgCl2 is 2:1. Therefore, there are 12 moles of Cl. There are 7.22×1024 atoms Cl in 3.61×1024 formula units of MgCl2 .