According to the law of conservation of mass, the total mass of the products in a chemical reaction is equal to the total mass of the reactants. In this case, the scientist is starting with 30 grams of calcium carbonate (CaCO3).
During the reaction, CaCO3 decomposes into carbon dioxide (CO2) and calcium oxide (CaO). Therefore, the total mass of the products will also be 30 grams.
The correct answer is:
30 grams