We have the number of moles of magnesium, now we will use the Avogadro number to determine formula units:
[tex]\text{Avogadro number = }6.022\text{ }\times10^{23}[/tex]Avogadro number says that one mole of a substance is equal to 6.022 × 10²³ units of that substance (such as atoms, molecules, or ions). Does not matter which is the substance, always 1 mol will be 6.022 x 10^23 formula units.
We have 1.27 moles so we will have:
[tex]1.27\text{ mol }\times\text{ }\frac{\text{6.022}\times10^{23}fu\text{.}}{1\text{ mol}}\text{ =}7.65\text{ }\times10^{23}formula\text{ units}[/tex]1.27 moles of magnesium are equivalent to 7.65 x 10^23 formula units