The number of atoms in a 12-g sample of carbon - 12 is called Avogadro's number (to which we give the symbol NA).
Recent measurements of this number give the value 6.0221367 x 1023, which is 6.023 x 1023.
A mole of a substance contains Avogadro's number of molecules. A dozen eggs equals 12 eggs, a gross of pencils equals 144 pencils and a mole of ethanol equals 6.023 x 1023 ethanol molecules.
The molecular mass of SO2 is 64 g mol-1. 64 g of SO2 contains 6.023 x 1023 molecules of SO2. 2.24 x 10-2m3 of SO2 at S.T.P. contains 6.023 x 1023 molecules of SO2.
Similarly the molecular mass of CO2 is 44 g mol-1. 44g of CO2 contains 6.023 x 1023 molecules of CO2. 2.24 x 10-2m3 of CO2 at S.T.P contains 6.023 x 1023 molecules of CO2.