Answer:
The answer to your question is the third choice.
Step-by-step explanation:
CaCO₃ ⇒ CaO + CO₂
Check if the reaction is balanced or unbalanced
Reactants Elements Products
1 Calcium 1
1 Carbon 1
3 Oxygen 3
As the number of atoms in the reactant is the same that the number of atoms in the products we conclude that the reaction is balanced.
So the correct answer is balanced because the total number of oxygen atoms is 3.