What is an example of a spontaneously combustible material?

A spontaneously combustible material is one that can ignite without an external flame or spark, typically due to a chemical reaction that produces enough heat to reach its ignition temperature. Potassium is a highly reactive alkali metal that reacts violently with moisture and air, generating heat and potentially leading to combustion.

When potassium is exposed to humid air, it can oxidize quickly and produce heat, which may cause it to ignite spontaneously. This characteristic distinguishes it from the other options listed, which are flammable liquids or gases. Although gasoline, hydrogen, and kerosene are all flammable and can be involved in combustion under the right conditions, they do not ignite spontaneously without an external ignition source. Understanding such distinctions is crucial for managing and transporting hazardous materials safely.