What is the question exactly?
The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. ... If we account for all reactants and products in a chemical reaction, the total mass will be the same at any point in time in any closed system.
Two moles of SO2 means 1.204x10^24 molecules, since there are 3 atoms in one molecule, multiply 1.204 x10^24 by 3 and you get 3.612x10^24.
