Which statement best describes the physical changes that occur when liquid water freezes and then melts again?

• A. Water undergoes a chemical reaction during freezing, forming a new substance, and then reverses the reaction during melting.
• B. Water evaporates during freezing and condenses during melting.
• C. Water's molecular structure is permanently altered during freezing and cannot return to its original state upon melting.
• D. Water changes from a liquid to a solid during freezing, and then back to a liquid during melting, with no change in chemical composition.

Answer: (D)

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 chemical properties.
2. Recognize that freezing and melting are phase changes involving water transitioning between liquid and solid states, which are physical changes because the chemical formula H\_2O remains the same.
3. Analyze the options: Freezing does not involve a chemical reaction or formation of new substances, so statements about chemical reactions or permanent molecular changes are incorrect.
4. Note that evaporation and condensation are phase changes between liquid and gas, not liquid and solid, so those options do not describe freezing and melting correctly.
5. Conclude that the best description is that water changes state from liquid to solid during freezing and back to liquid during melting, with no change in chemical composition, which is a physical change.