G2 Gas Fitter Exam 2026 – 400 Free Practice Questions to Pass the Exam

Nitrogen is considered an inert substance in the context of combustion. Inert gases do not react chemically during the combustion process, which means they do not contribute to combustion itself but can affect combustion characteristics.

In practical applications, nitrogen makes up about 78% of the Earth's atmosphere and is typically present in combustion processes. As it passes through the combustion zone, it absorbs heat without participating in the chemical reaction, which can help regulate combustion temperatures and prevent excessive thermal buildup.

Other substances included in the options have different roles in combustion. Carbon dioxide, for instance, is a product of combustion rather than an inert element and can influence the flame characteristics. Hydrogen, while it burns and produces heat, is not inert as it actively participates in combustion reactions. Ozone, though it can be a reactive gas, is not relevant in most combustion scenarios and generally does not act as a stable inert substance in that environment.

Thus, because nitrogen does not react chemically but absorbs heat, it is the correct answer to the question regarding a substance that is inert while passing through the combustion zone.