An atom of gold has a mass of 3.271 x 10^-22g. how many atoms of gold are in 5.00g of gold?

5.00g Au x (1 atom Au/3.271x10^-22 g) = 1.52858x10^22 atoms

Since one of your given terms has only 3 significant figures (5.00g), your answer should only have 3 sig figs showing: 1.53x10^22 atoms Au