Which properties occur without a chemical reaction?

Physical properties occur without a chemical reaction because they describe the characteristics of a substance as it exists in its unaltered state. These properties include color, boiling point, melting point, density, and solubility, among others. They can be observed or measured without changing the chemical composition of the material. For instance, measuring the boiling point of water does not change its chemical identity; it remains water, H₂O, regardless of its state (liquid or gas).

In contrast, chemical properties pertain to a substance's ability to undergo chemical changes and transformations into different substances, which involves a chemical reaction. Reactive properties typically refer to the tendency of a substance to react chemically with another substance, implying that a chemical change occurs. Invariant properties usually refer to characteristics that do not change regardless of the circumstances but are not commonly recognized as a distinct category in the same way physical properties are.

Thus, physical properties are the correct answer as they manifest without any chemical transformation taking place.