Final answer:
The mass of the original candle and the oxygen that reacted equals the mass of the burned candle plus the mass of the gases released during the burning, according to the Law of Conservation of Mass.
Step-by-step explanation:
When a candle is burned in oxygen in a closed system, the Law of Conservation of Mass states that the mass of the reactants (the candle and the oxygen) must equal the mass of the products. So, if we were to measure the mass of the original candle and the mass of the oxygen that reacted with it, we would find that it is exactly equal to the mass of the leftover wax (the burned candle) plus all the gases released while the candle burned, which in this case includes compounds such as carbon dioxide and water vapor.
Therefore, the correct answer is option 4: The mass of the burned candle plus the mass of the gases released while the candle is burned. This is because even though the physical state of the candle has changed after burning, no matter is lost or created in the process.