Which of the following is an example of a flammable solid?

Magnesium is classified as a flammable solid because it can ignite and burn in the presence of heat and oxygen. When powdered or in thin strips, magnesium can burn brightly and emit a white light, and it requires careful handling to prevent accidental ignition. This property makes it necessary to store and manipulate magnesium in controlled conditions, especially in laboratory settings where the use of flammable substances is common.

The other substances listed do not meet the criteria for flammable solids. Water is an inorganic compound that does not burn and is often used to extinguish fires. Oil, while flammable, is classified as a flammable liquid rather than a solid. Glass is an inorganic material that is not flammable at all. Understanding these classifications is crucial for laboratory safety and proper handling of materials.