Which of these elements does not support combustion?

Carbon dioxide is the correct answer because it does not support combustion. In the combustion process, a fuel (such as wood or gasoline) reacts with oxygen to produce energy in the form of heat and light. Oxygen is essential for combustion, as it acts as an oxidizer that allows the fuel to burn. Heat serves to raise the temperature of the fuel and promote the chemical reactions necessary for combustion.

In contrast, carbon dioxide is produced as a byproduct of combustion and actually inhibits the process. It does not contribute to or sustain combustion; rather, it can extinguish flames by removing oxygen from the vicinity of the fuel. Therefore, carbon dioxide stands out as the element that does not support combustion, while the other options are integral to the combustion process.