When two substances are mixed together, a color change is observed. does this mean that a chemical reaction has definitely occurred? - yes because any change indicates a chemical reaction. - no because some physical changes produce color changes. - no because color changes are not indicators of chemical reactions. - yes because color changes occur only when new compounds are formed.

 No because some physical changes produce color changes.

Explanation:-

A physical reaction is defined as the reaction in which a change in shape, size takes place. No new substance gets formed in these reactions.

Example: Addition of food colors to water is a physical process and lead to color change

A chemical reaction is defined as the reaction in which a change in chemical composition takes place. A new substance is formed in these reactions.

Example: Oxidation of magnesium leads to formation of white magnesium oxide and is a chemical change.