In physical science, what does the term "physical change" refer to?

The term "physical change" refers to alterations that do not affect the chemical composition of a substance. This means that during a physical change, the original substance remains unchanged at the molecular level, allowing it to retain its chemical properties. Examples of physical changes include melting ice into water, dissolving sugar in water, or breaking glass. In each of these instances, the substance itself is still identifiable chemically, and no new substance is formed.

The other options define different types of changes. A modification in the molecular structure pertains to chemical changes where new substances are produced. A change leading to a new substance is also a characteristic of a chemical change, while an irreversible transformation signifies that a substance cannot easily revert to its original form, which again aligns with chemical changes rather than physical ones. Thus, the definition emphasizing the non-altering impact on chemical composition is what aligns perfectly with the correct answer.