Burning a candle is a combustion reaction that uses wax and oxygen to produce carbon dioxide, water, and energy. when you burn a candle down in an open room, the limiting reactant is

The wax

Explanation:

The limiting reactant is the reactant in short supply in a particular reaction. This reactant determines the extent of the reaction. Oxygen in the reaction is the one in excess. As we know that oxygen is free in the atmosphere and it is in excess supply.

After the wax finishes burning the reaction stops and no more production of carbon dioxide, water and energy but oxygen still continues to abound all around.

In order to determine the amount of carbon dioxide and water that would be produce, we simply use the amount of wax to relate with them.