What defines a physical change in a substance?

A physical change in a substance is characterized by alterations that do not affect its chemical identity. This means that the substance retains its original properties and composition, despite undergoing changes in form, state, or appearance. Examples include melting ice into water or breaking a glass. In these instances, even though the substance may change shape or state, it remains fundamentally the same substance.

The other options describe different types of changes. A change in chemical composition indicates a chemical change, where new substances are formed. An alteration that alters the identity of the substance also refers to a chemical change, as it involves a transformation that results in a different substance. A permanent change in color can sometimes signal a chemical change as well, particularly if it indicates a reaction has occurred. Thus, the core aspect of a physical change is that it does not affect the chemical identity of the substance itself.