Calcium carbonate can break down to form calcium oxide and carbon dioxide.CaCO3 → CaO + CO2The oxygen atoms on the product side are

Count the oxygen atoms on each side of the equation. CaCO₃ has 3 oxygen atoms, while the products have 1 in CaO and 2 in CO₂, for a total of 3. The oxygen atoms are balanced, so the correct choice is “balanced because the total number of oxygen atoms is 3.”

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