Which molecule is considered a fuel for combustion?

Hydrogen is considered a fuel for combustion because it can react with oxygen to produce water and energy in the form of heat. This exothermic reaction is a fundamental principle of combustion, where a fuel combines with an oxidizer (typically oxygen) to release energy. In the case of hydrogen combustion, it is one of the cleanest fuels, producing only water vapor as a by-product, which is a significant advantage in terms of environmental impact.

In contrast, carbon dioxide is a product of combustion rather than a fuel, as it results from the burning of carbon-based fuels. Oxygen, while essential for combustion as an oxidizer, does not act as a fuel itself because it does not produce energy when burned. Nitrogen does not participate in combustion reactions; it is generally inert under normal conditions and does not contribute to the energy release associated with burning fuels. Thus, hydrogen is the only molecule listed that serves as a fuel in combustion processes.