The correct response to how the balanced chemical equation \( 4Fe + 3O_2 \rightarrow 2Fe_2O_3 \) shows the law of conservation of mass is:
The number of atoms of each element is the same on both sides.
This is because, in the equation, there are 4 iron (Fe) atoms and 6 oxygen (O) atoms on both the reactant side and the product side, demonstrating that mass is conserved during the reaction.