Final answer:
The statement is true according to the law of conservation of mass, which states that in a chemical reaction, the mass of the reactants equals the mass of the products. However, in nuclear reactions, mass can be converted into energy, making this an exception.
Step-by-step explanation:
No mass is lost when the reactants turn into products; this statement is true because it aligns with the law of conservation of mass. This fundamental principle of chemistry states that in any chemical reaction, the mass of the substances that react equals the mass of the products that are formed. The mass of the reactant is always equal to the mass of the products, which is an observable phenomenon that supports this law.
In chemical reactions, the composition and number of atoms are preserved from reactants to products, meaning there is nothing in the products that did not originate in the reactants. It's worth noting, however, that in nuclear reactions such as fusion and fission, the mass of the products can be different due to the conversion of mass into energy as per Einstein's equation E=mc^2. In such cases, the mass change is often measurable, but this is an exception to typical chemical reactions.