A balloon contains 7.36 g of oxygen gas (O2). How many oxygen molecules are in the balloon?

To find the number of oxygen molecules in the balloon, you can first calculate the number of moles of O2 using its molar mass (32 g/mol). Then, use Avogadro's number (6.022 x 10^23 molecules/mol) to convert moles to molecules. In this case, the balloon contains approximately 1.15 x 10^23 oxygen molecules.