The true statement regarding a chemical reaction is: "the total number of atoms does not change, so mass is conserved in the reaction."
In a chemical reaction, according to the law of conservation of mass, the total mass of the reactants is equal to the total mass of the products, meaning that mass is conserved. Additionally, atoms are neither created nor destroyed in a chemical reaction; they are merely rearranged. Therefore, while the substances may change, the total number of each type of atom remains constant, leading to the conservation of mass.