Let's analyze the reaction you provided:
\[ \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \]
On the reactant side (left), there is 1 calcium atom (Ca), 1 carbon atom (C), and 3 oxygen atoms (O) in calcium carbonate (CaCO₃).
On the product side (right), there is 1 calcium atom in calcium oxide (CaO), 1 carbon atom in carbon dioxide (CO₂), and 2 oxygen atoms in carbon dioxide (CO₂), plus 1 oxygen atom in calcium oxide (CaO). This means there are a total of:
- 1 Ca from CaO
- 1 C from CO₂
- 2 O from CO₂ + 1 O from CaO = 3 O
The total number of atoms is:
- Calcium: 1 (from CaO)
- Carbon: 1 (from CO₂)
- Oxygen: 3 (total from CaO and CO₂)
Therefore, the oxygen atoms are balanced overall because each side has 3 oxygen atoms.
So, the correct answer is: balanced because the total number of oxygen atoms is 3.