How many atoms are there in 5.70 mol of mg

1st we need to find out how many atoms are in 1 mol of Mg

we can access this on our periodic tables (easily enough).  It is the atomic # (above the Mg)... this means that:

{(12 atoms of Mg) / ((6.022x10^23 atoms of Mg / 1 mol of Mg)}

will tell us how many atoms are in ONE mol of Mg  but we need to find out how many atoms are in 5.70 mols! ... so lets factor this in at the end of that initial equation...  

{above} x 5.70 mols of Mg

(This way, when written out, we can see how the mols of Mg cancel out, and therefore, we have our final answer in Atoms of Mg

Hope that was helpful!!

^-^ (don't forget to utilize Avagadro's # whenever asked to switch between mols, atoms, grams, and the like! It is like magic ;-P)