•There are 3 molecules in the formula 3H2SO4
Explanation: H2SO4 is one molecule and the number 3 shows there are 3 molecules
•There are 4 Al atoms in the formula 2Al2(CO3)3
Explanation: It shows there are 2 molecules of Al2(CO3)3 and each of those molecules has 2 Al atoms, so in total there are 2x2 Al atoms= 4 Al atoms
•There are 9 Total atoms in the formula 3MgBr2
Explanation: There are 3 molecules of MgBr2 and each molecule has 1 Mg atom and 2 Br atoms = 3 atoms for each molecule. The 3 molecules have 3x3 atoms = 9 atoms