Which of the following is an indicator of a chemical change?

A color change is a strong indicator of a chemical change because it often suggests that new substances have formed as a result of a chemical reaction. During a chemical change, bonds between atoms in the original substances break and new bonds form, resulting in entirely new products that can have different colors compared to the reactants. For example, the rusting of iron leads to a color change from metallic grey to reddish-brown, indicating a chemical reaction has taken place.

In contrast, options such as freezing point and melting point are physical properties of substances that do not involve a change in the chemical composition of the material. These properties are associated with the phase changes of matter (solid to liquid and vice versa) and do not indicate that a chemical reaction has occurred. Mass, while a measure of quantity, also does not indicate a chemical change, as it remains the same before and after a reaction (when considering closed systems). Therefore, color change is a clear and observable sign of a chemical change occurring.