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

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

Answer: (D)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: Physical changes affect the form of a substance but not its chemical composition, while chemical changes result in the formation of new substances with different properties.
2. Analyze each option to determine if it indicates a physical or chemical change: Change in shape is a physical change because the substance's identity remains the same.
3. Dissolving sugar in water is a physical change since sugar molecules disperse but do not chemically react or form new substances.
4. Melting of a solid is a physical change because it involves a phase change without altering the chemical identity of the substance.
5. Formation of a gas is a strong clue of a chemical change because it often indicates a chemical reaction producing a new substance, such as gas bubbles forming during a reaction.