Which of the following is a common indication that a chemical reaction has occurred?

• A. A change in color is observed.
• B. The temperature of the surroundings remains constant.
• C. The substance dissolves in water without any other change.
• D. The substance is simply broken into smaller pieces.

Answer: (A)

Verified step by step guidance

1. Understand that a chemical reaction involves the formation of new substances with different properties from the original substances.
2. Recognize that common indications of a chemical reaction include changes such as color change, temperature change, gas production, formation of a precipitate, or emission of light.
3. Analyze each option: a change in color suggests a new substance is formed, indicating a chemical reaction.
4. Note that if the temperature remains constant, it does not necessarily indicate a chemical reaction, as some reactions are exothermic or endothermic and cause temperature changes.
5. Understand that dissolving without other changes and breaking into smaller pieces are physical changes, not chemical reactions, because the substance's identity remains the same.