Which of the following describes the physical properties of matter?

The choice that describes the physical properties of matter correctly is indeed characterized by properties that can be observed or measured without changing the substance's chemical identity.

Physical properties are attributes that can be determined without altering the composition of the material. For instance, color describes the appearance of a substance, odor refers to its smell, shape indicates its geometric form, and hardness describes how resistant it is to deformation. These properties relate directly to how a material behaves or appears in its pure state.

In contrast, other options include properties like reactivity (the ability of a substance to undergo a chemical reaction), acidity, and flammability, which are chemical properties that involve changes in the substance's chemical structure. Thus, they do not fit under the definition of physical properties. The focus in the correct answer on observable traits aligns perfectly with the understanding of physical properties in the study of matter.