Which of the following is a clue that a chemical change has taken place?

• A. Change in shape
• B. Melting of a solid
• C. Formation of a gas
• D. Dissolving sugar in water

Answer: (C)

Verified step by step guidance

1. Understand the difference between physical and chemical changes. A physical change affects the form of a substance but not its chemical composition, while a chemical change results in the formation of new substances with different properties.
2. Analyze each option to determine if it represents a physical or chemical change:
3. 1. Change in shape: This is a physical change because the substance's identity remains the same despite the change in form.
4. 2. Melting of a solid: This is a physical change where a solid turns into a liquid without altering its chemical composition.
5. 3. Formation of a gas: This often indicates a chemical change because new substances (gases) are produced, which is a sign of a chemical reaction.
6. 4. Dissolving sugar in water: This is a physical change where sugar molecules disperse in water but do not chemically react or form new substances.