Which of the following demonstrates a chemical change?

• A. Ice melting into liquid water
• B. Rust forming on an iron nail
• C. Breaking a glass window
• D. Salt dissolving in water

Answer: (B)

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 one or more new substances with different properties.
2. Analyze each option to determine if the substance's chemical identity changes:
3. 1. Ice melting into liquid water: This is a phase change where solid water becomes liquid water, but the chemical formula H\_2O remains the same, so it is a physical change.
4. 2. Rust forming on an iron nail: This involves iron reacting with oxygen and moisture to form iron oxide (rust), which is a new substance, indicating a chemical change.
5. 3. Breaking a glass window: This changes the shape and size of the glass but does not alter its chemical composition, so it is a physical change.
6. 4. Salt dissolving in water: The salt dissociates into ions but does not chemically change; it can be recovered by evaporating the water, so this is a physical change.