Which gas does not support combustion?

Nitrogen is recognized for its inert properties and is known for not supporting combustion. When discussing combustion, it is important to understand that a gas needs to be reactive with oxygen to support the process. Nitrogen makes up approximately 78% of the Earth's atmosphere and serves as a non-reactive component that can act as a diluting agent to prevent combustion.

In contrast, gases such as oxygen and carbon dioxide play critical roles in combustion reactions. Oxygen is a vital reactant that fuels the burning process, while carbon dioxide is often a product of combustion but can also participate in certain combustion processes in specific scenarios. Helium, while also inert, does not possess the same commonality or presence in the atmosphere compared to nitrogen and is not typically involved in combustion processes.

Thus, nitrogen's role as a non-combustible gas makes it the definitive answer to this question regarding which gas does not support combustion.