In the reaction of heating calcium carbonate (CaCO3), it decomposes into calcium oxide (CaO) and carbon dioxide (CO2) according to the equation:
\[ \text{CaCO}_3 (s) \rightarrow \text{CaO} (s) + \text{CO}_2 (g) \]
When working with reactions, we can apply the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. The total mass of the reactants must equal the total mass of the products.
In this case, if you start with 30 grams of calcium carbonate (CaCO3), the total mass of the products (calcium oxide and carbon dioxide) will also be 30 grams.
Thus, the correct response is:
30 grams