Which explains the law of conservation of mass? a. Every reaction creates an equal amount of mass related to the amount of
energy required for the reaction.
b. The total mass before a chemical reaction is the same as the total mass after
the reaction.
c. Matter can not be conserved.
d. The total amount of mass is equal to the volume of both chemicals in the
reaction.

A is your answer.

Explanation:

This law states that, despite chemical reactions or physical transformations, mass is conserved — that is, it cannot be created or destroyed — within an isolated system. In other words, in a chemical reaction, the mass of the products will always be equal to the mass of the reactants.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)