Which of the following is a commonly accepted indicator that a chemical reaction has occurred?

• A. Change in color
• B. Change in temperature
• C. Dissolving of a solid in water
• D. Formation of a gas

Answer: (D)

Verified step by step guidance

1. Understand that a chemical reaction involves the rearrangement of atoms to form new substances, often accompanied by observable changes.
2. Identify common indicators of chemical reactions, such as changes in color, temperature, formation of a gas, or formation of a precipitate.
3. Recognize that dissolving a solid in water is usually a physical change, not a chemical reaction, because the substance's chemical identity remains the same.
4. Note that a change in color indicates a new substance with different properties has formed, signaling a chemical reaction.
5. Understand that a change in temperature (exothermic or endothermic) and the formation of a gas are also signs that a chemical reaction has taken place.