Which of the following is an indicator that a chemical reaction is occurring?

• A. Dissolving of a solid in water without any other change
• B. Change in color
• C. Change in temperature
• D. Formation of a gas

Answer: (D)

Verified step by step guidance

1. Understand that a chemical reaction involves the rearrangement of atoms and results in the formation of new substances with different properties.
2. Identify common indicators of chemical reactions, which include changes that suggest new substances are being formed, such as a change in color, change in temperature, or formation of a gas.
3. Recognize that dissolving a solid in water without any other change is a physical change, not a chemical reaction, because no new substance is formed.
4. Note that a change in color can indicate a chemical reaction because it often reflects a change in the chemical composition of the substances involved.
5. Understand that a change in temperature (exothermic or endothermic) and the formation of a gas are also signs that a chemical reaction is taking place, as energy is absorbed or released and new gaseous products may form.