The correct statement about the reaction \( 2H_2O_2 \rightarrow 2H_2O + O_2 \) is:
C. the H2O and O2 produced have the same mass as the original H2O2.
This is due to the law of conservation of mass, which states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products. Therefore, the mass of the H2O and O2 produced is equal to the mass of the original H2O2 that decomposes in the reaction.