Which sample contains the greatest # of atoms?

Greatest number of atoms....

The solution to this problem involves calculating the number of atoms in each sample. But we can instead calculate the moles, since one mole of atoms is equal to 6.022x10^23 atoms. The element with the greatest number of moles will have the greatest number of atoms. In fact, we will find that all of the elements but one will have less than a mole, with only one being more than a mole.

91g Mo x (1 mol Mo / 95.95 g Mo) = .... less than 1 mole

18.0g O x (1 mol O / 16.0g O) = .... MORE than 1 mole

102g Ag x (1 mol Ag / 107.9g Ag) = .... less than 1 mole

34g K x (1 mol K / 39.1g K) = .... less than 1 mole