What type of substances are classified as liquid fuels?

Liquid fuels are substances that are in a liquid state at room temperature and have the ability to ignite and burn when exposed to an ignition source. These flammable liquids release vapors that can readily mix with air, and when the concentration of these vapors is within a certain range, they can ignite, resulting in combustion. Examples include gasoline, diesel, and alcohol. The ability of these substances to produce flames and support combustion is a key characteristic that qualifies them as liquid fuels.

The other options reflect materials that either do not have the capacity to support combustion, like non-flammable gases and inert materials, or represent a different state, such as solid materials, which do not classify as liquid fuels. Understanding the nature of liquid fuels is essential for firefighting and safety protocols, particularly in recognizing the risks and behaviors of various substances in a fire scenario.