Question: Which of the following molecules contain ...?

There are 6.022 x 10^23 molecules of a compound in 1 mole of that compound. To determine the weight of 1 mole simply add the atomic weights of each of the elements it contains remembering to multiply by any subscript. You can then divide the amount of the compound you have by the gram-molecular weight to get the number of moles. The last step is to determine the number of atoms in a molecule which can be done by adding all of the subscripts in the chemical formula (use 1 if there is no subscript).