Which of the following is true regarding the law of conservation of mass

These are the answer options of this question and the comments about their validity:

A) It dictates that the number of molecules on each side of a chemical equation must be the same.

False: the number of molecules can change. Take this simple reaction for example:

2H2(g) +  O2 -> 2H2O

You start with 3 molecules, 2 molecules of H2 and 1 molecule of O2, and end with 2 molecules of water. Then the number of molecules of each side is different.

B) It dictates that the number of atoms of each element must be the same on both sides of a chemical equation.

TRUE: in a chemical reaction the atoms remain being the same at start and at the end of the process. Given that each atom has a characteristic mass, their conservation implies the law of conservation mass.

C) It states that the mass of the reactants must remain constant in order for a chemical reaction to proceed.

FALSE. The mass of the reactants changes during a chemical reaction, while they transform into the products.

D) It does not apply to chemical reactions.

FALSE: It is an important law used in the calculus related with chemical reactions.