Question

A sample of barium contains 3.20g of barium. How many atoms of barium are contained in the sample?

Answer 1

How many mols do you have? That's mols = grams/molar mass = approx 0.023 but you need to do it more accurately.
Then 1 mol contains 6.02E23 atoms. So 0.023 mols will contain ...... atoms.