Final answer:
The mass after the reaction should be 140 grams.
Step-by-step explanation:
The Law of Conservation of Mass states that during a chemical reaction, the total mass of the reactants is equal to the total mass of the products. In this case, the mass before the reaction was 140 grams. According to the Law of Conservation of Mass, the mass after the reaction should also be 140 grams, option (a).