Which property of a substance can be observed without altering its chemical identity?

The observation of a physical property refers to characteristics of a substance that can be identified without changing its chemical structure or composition. Examples of physical properties include color, density, melting point, boiling point, and state of matter (solid, liquid, or gas). When a physical property is measured or observed, the substance itself remains the same at the molecular level; it does not undergo any chemical reaction or transformation.

In contrast, a chemical property describes how a substance interacts with other substances, resulting in a change in its chemical identity. This could include reactions such as combustion, rusting, or acidity, all of which alter the substance at a molecular level. Intramolecular and atomic properties refer more specifically to the nature of molecules or atoms within a substance, potentially involving chemical changes.

Therefore, the property that allows observation without altering the chemical identity of a substance is indeed a physical property.