What is an example of a physical change?

The correct answer is an example of melting ice, which is a physical change because it involves a transition from a solid state to a liquid state without altering the chemical composition of the substance. When ice melts, it changes from solid water (ice) to liquid water, but both forms are still water (H2O) at the molecular level. This illustrates how physical changes are typically reversible and do not create new substances.

In contrast, rust forming on metal is a chemical change because it involves a reaction between iron, oxygen, and moisture that results in iron oxide, a new compound. Burning wood is also a chemical change as it results in the formation of ash, gases, and other substances through combustion. Lastly, digestion of food represents a series of chemical changes that break down complex food molecules into their simpler forms, resulting in new substances that can be absorbed by the body. All of these processes involve changes at the molecular level that create new materials, which distinguishes them from physical changes like melting ice.