The mass of 1 mole of a compound is equal to its atomic weight, in grams. For example, 1 mole of water (H2O) has 2×1+16=18 grams mass. Avagadro's Law: The volume of 1 mole of any gas (stp) = 22.4 liters
So 22.4 litres has 1 mole of any gas then
22.4litre = 1mole
So 1 litre=122.4litre
Therefore, 33.6 litres contains (122.4)×33.6 moles=1.5 moles.