Question

1. which statement is always true about conservation of mass?

a. the total mass of the reactants is equal to the total mass of the products.
b. the mass of one reactant is equal to the mass of one product.
c. the total mass of a system changes in a chemical reaction.
d. the mass changes in a phase change, but not in a chemical reaction.

Explanation:

The law of conservation of mass states that in a closed system, the total mass of reactants before a chemical reaction is equal to the total mass of products after the reaction. Option B is incorrect because individual reactants and products don't have to have equal masses. Option C is wrong as the total mass of a system remains constant in a chemical reaction. Option D is incorrect because mass is conserved in both phase changes (physical changes) and chemical reactions. So only option A aligns with the conservation of mass principle.

Answer:

A. The total mass of the reactants is equal to the total mass of the products.