So in order to answer this question you need to know how many moles are in 36.8g of magnesium. A mole of magnesium has a mass of 24.3 grams. 36.8/24.3 is about 1.51. This is how many moles are in 36.8 g of magnesium. Now you multiply this number by Avagadro's number which is 6.022E23. The total should be 9.12E23 atoms of magnesium.