In a chemical reaction, the law of conservation of mass states that mass is neither created nor destroyed; the total mass of the reactants must equal the total mass of the products.
In this case, the scientist starts with 30 grams of calcium carbonate (CaCO₃). Upon heating, this compound decomposes into carbon dioxide (CO₂) and calcium oxide (CaO).
Since no mass is lost in the reaction, the total mass of the products will be equal to the mass of the reactants. Therefore, the total mass of the products will be:
30 grams
So the correct response is:
30 grams.