Question

How many atoms are present in 48.60 g of Mg

Answer 1

1.204 x 10 ( 24 ) atoms of magnesium are present.
In order to go from mass of magnesium there have to do 2 things 

1. convert mass of Mg to moles of Mg using the molar mass of Mg as converted to a factor 

2. convert moles of Mg to atoms of Mg using the Avogadro's number ( 6.02 x 10  (23) as a conversion factor 
 
Hope my it helped a little :)