Which statement best distinguishes a chemical change from a physical change?

• A. It forms new substances.
• B. It changes only the appearance.
• C. It is always reversible.
• D. It involves no energy change.

Answer: (A)

What distinguishes a chemical change is that new substances with different properties are formed. When bonds break and new ones form, the material you started with is transformed into something chemically different, like iron reacting with oxygen to become rust, or baking a cake where ingredients become a new product. A physical change, by contrast, changes how the substance looks or behaves without making a new substance—for example ice melting into water or sugar dissolving in water, where the chemical composition stays the same.

So the statement that best captures the distinction is that a chemical change forms new substances. The other ideas aren’t reliable indicators: changes in appearance can happen in both types, reversibility isn’t guaranteed for chemical changes, and chemical changes often involve energy changes, not none.