Which property is only observable at a molecular level?

The correct answer is that a chemical property is only observable at a molecular level because it pertains to the potential of a substance to undergo chemical changes, which can only be detected by observing the behavior and reactivity of the molecules or compounds under specific conditions. Examples of chemical properties include reactivity with other chemicals, flammability, and acidity, all of which require interaction at the molecular level to assess.

In contrast, physical properties can typically be observed and measured without causing a change in the substance, such as color, melting point, and density, and are often observable at a macroscopic level. Macroscopic properties refer to those that can be seen and measured directly, such as volume or mass, while subatomic properties relate to particles even smaller than molecules, like electrons and protons, which are not typically considered when discussing molecular interactions and behaviors.