Which phenomenon is described as not being a physical occurrence?

A chemical reaction is described as not being a physical occurrence because it involves a transformation of substances at the molecular level, resulting in the formation of new chemical products. This change often alters the chemical composition and properties of the reactants, distinguishing it from physical occurrences, which typically involve changes in state or appearance without altering the substance's fundamental chemical identity.

In contrast, temperature fluctuation refers to changes in a physical property that can easily be measured and does not involve a change in the chemical structure of a substance. Similarly, force application involves physical interactions between objects that affect their motion or deformation, and mass measurement pertains to the determination of the amount of matter present in an object or substance. These phenomena are observable and may not involve any change in the chemical nature of the materials involved.