* Na2SO4: This represents one molecule of sodium sulfate.

* 3Na2SO4: This means we have 3 molecules of sodium sulfate.

Counting the Atoms:

* Sodium (Na): There are 2 sodium atoms per molecule, and we have 3 molecules, so that's 2 * 3 = 6 sodium atoms.

* Sulfur (S): There is 1 sulfur atom per molecule, and we have 3 molecules, so that's 1 * 3 = 3 sulfur atoms.

* Oxygen (O): There are 4 oxygen atoms per molecule, and we have 3 molecules, so that's 4 * 3 = 12 oxygen atoms.

Total Atoms: 6 + 3 + 12 = 21 atoms

Therefore, there are 21 total atoms in 3Na2SO4.