Oxygen gas has the following molecular formula: O2.
According to this, its molar mass is 32g/mol.
Use this information to find how many grams are there in one mole of oxygen gas:
[tex]1molO_2\cdot\frac{32gO_2}{molO_2}=32gO_2[/tex]It means that there are 32g of oxygen gas in one mole of this gas.