Which of the following changes is NOT a physical state change?

• A. Melting
• B. Combustion
• C. Sublimation
• D. Condensation

Answer: (B)

Combustion is the process that involves a chemical reaction, typically between a fuel and an oxidant, resulting in the release of energy in the form of heat and light. This reaction fundamentally alters the chemical structure of the substances involved, leading to the formation of new compounds, such as carbon dioxide and water when hydrocarbons combust. This transformation signifies a change in the chemical composition, rather than just a physical state.

On the other hand, melting, sublimation, and condensation are all physical changes because they involve transitions between different states of matter (solid, liquid, gas) without altering the chemical identity of the substances involved. For instance, melting changes a solid to a liquid, sublimation switches a solid directly to a gas, and condensation turns a gas into a liquid, all while maintaining the original compound. Thus, the identification of combustion as the change that is not a physical state change is accurate.