Which of the following is an example of a physical change?

A physical change is a transformation that alters the form or appearance of a substance but does not change its chemical composition. Melting ice is a classic illustration of a physical change because it simply transitions from a solid state (ice) to a liquid state (water) when heat is applied. Throughout this process, the chemical structure of H2O remains unchanged; it is still water in both solid and liquid forms. This is what distinguishes a physical change from a chemical change, which would involve a complete transformation of the substance into new materials with different properties.

In contrast, burning wood, rusting iron, and digesting food all involve chemical changes. These processes result in the creation of new substances, such as ash and gases from burning wood, iron oxide from rusting, and various simpler compounds from digesting food. Thus, while those examples indicate transformations, they fundamentally change the materials involved.