Which of the following describes a physical reaction?

A physical reaction is characterized by changes that affect the form of a substance but not its chemical composition. In the context of this question, maintenance of the compound's molecular structure aligns with the definition of a physical reaction.

When a reaction is described as maintaining the molecular structure, it indicates that the identity of the compound remains the same throughout the process. For example, phase changes such as melting, freezing, or boiling are physical reactions because they involve transitions between solid, liquid, and gaseous states without altering the chemical bonds or the molecular composition of the substance itself.

In contrast, the formation of new compounds involves chemical reactions where new bonds are created, resulting in different substances. Breaking chemical bonds also signifies a chemical change because it leads to the formation of new products. Similarly, a change in molecular structure typically suggests a rearrangement of atoms and bonds that occurs during a chemical reaction, thus altering the compound's identity. These characteristics collectively help differentiate physical reactions from chemical ones, confirming that maintaining the compound's molecular structure is indeed a hallmark of a physical reaction.