Which of the following is classified as a fuel gas?

Propane is classified as a fuel gas because it is a hydrocarbon that is commonly used as a source of energy for heating, cooking, and fueling vehicles. Fuel gases are typically combustible gases that can easily ignite and produce heat when burned. Propane is stored in liquid form under pressure and vaporizes when released, making it readily available for combustion in various applications.

In contrast, hydrogen is also a fuel gas but may not be as widely recognized in common usage as propane, which is more prevalent in residential and commercial settings. Nitrogen, on the other hand, is an inert gas and does not support combustion, while oxygen, though crucial for combustion, is not considered a fuel gas itself. Fuel gases are specifically those that can sustain combustion to produce energy, which is why propane clearly fits the definition as a fuel gas.