Which of the following conditions is an example of a chemical change?

• A. Water boiling to form steam
• B. Salt dissolving in water
• C. Ice melting into liquid water
• D. Iron rusting when exposed to moisture

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 the substance's chemical identity changes:
3. 1. Water boiling to form steam: This is a phase change from liquid to gas, but the chemical formula H\_2O remains the same, so it is a physical change.
4. 2. Salt dissolving in water: The salt dissociates into ions but does not change its chemical identity, so this is a physical change.
5. 3. Ice melting into liquid water: This is a phase change from solid to liquid, with no change in chemical composition, so it is a physical change.
6. 4. Iron rusting when exposed to moisture: This involves iron reacting with oxygen and water to form iron oxide, a new substance, indicating a chemical change.