# How many moles of Cl are in 1.2 * 10^24 formula units of magnesium chloride?

$\text{4.0 mol}$ of ${\text{Cl}}^{-}$ ions.
Magnesium chloride is an ionic compound with an ${\text{Mg}}^{2 +}$ ion and two ${\text{Cl}}^{-}$ ions in each formula unit. Thus:
$1.2 \cdot {10}^{24} \text{ formula units" * ("1 mol MgCl"_2)/(6.023*10^23 " formula units")*("2 mol Cl"^(-) " ions")/("1 mol MgCl"_2) = "2.0 mol Cl"^(-) " ions}$