Which of the following is evidence of a chemical reaction?

• A. Evaporation of water
• B. Dissolving sugar in water
• C. Change in state from solid to liquid
• D. Formation of a precipitate

Answer: (D)

Verified step by step guidance

1. Understand that a chemical reaction involves the formation of new substances with different properties, often accompanied by observable changes such as color change, gas production, temperature change, or formation of a solid (precipitate).
2. Analyze each option to determine if it represents a physical change or a chemical change. Physical changes involve changes in state or appearance without forming new substances, while chemical changes produce new substances.
3. Recognize that evaporation of water is a physical change because it involves a change from liquid to gas without altering the chemical identity of water.
4. Identify that dissolving sugar in water is also a physical change because sugar molecules disperse in water but do not chemically react to form new substances.
5. Note that the formation of a precipitate indicates a chemical reaction because it involves the creation of an insoluble solid from a solution, which is evidence of new substance formation.