Question

which of the following would provide the evidence that the number of atoms present before a chemical reaction is equal to the number of atoms present after the chemical reaction?
bubbles were produced during the reaction, which meant that a gas was being produced.
the mass of the baking soda was exactly equal to the mass of the vinegar used to create the chemical reaction.
the mass of the plastic bag, baking soda, and vinegar before the reaction was equal to the mass after the reaction.
the plastic bag did not change in any way, indicating that it was not involved in the reaction.

Explanation:

According to the law of conservation of mass, in a chemical reaction, the total mass of reactants is equal to the total mass of products. The statement "The mass of the plastic bag, baking soda, and vinegar before the reaction was equal to the mass after the reaction" shows that the total mass (which is related to the number of atoms as mass is proportional to the amount of matter - atoms in this case) remained the same before and after the reaction. This implies that the number of atoms (since atoms contribute to mass) is conserved (same before and after reaction).

Answer:

The mass of the plastic bag, baking soda, and vinegar before the reaction was equal to the mass after the reaction.