Combustible substances are materials that can easily catch fire and burn when exposed to heat or flames. Common examples include wood, paper, and certain types of fuels like gasoline. These substances contain carbon and hydrogen, which react with oxygen during combustion, producing heat, light, and various gases. The ability of a substance to combust depends on its chemical composition and physical state. For instance, solids like wood require a higher temperature to ignite compared to liquids like gasoline. Understanding combustible substances is essential for safety in environments such as homes, workplaces, and industrial settings.