Which of the following materials is classified as a Class D combustible?

Class D combustibles are defined as metals that can ignite and burn in the presence of oxygen and can cause violent reactions when they come into contact with water or certain other substances. Sodium is a highly reactive metal and fits this classification. It can catch fire easily and burn with a bright flame when exposed to moisture or water, making it a prime example of a Class D combustible.

In contrast, gasoline, wood, and paper do not fall under the Class D category. Gasoline is classified as a Class B combustible due to its flammability as a liquid and potential to form explosive vapors. Wood and paper are organic materials that are classified as Class A combustibles. They ignite from heat and burn in a more conventional manner compared to metals like sodium. This distinction is crucial for understanding fire safety and the appropriate response to different types of combustible materials.