Answer: expand.
- A expand
- B contract
- C disappear
- D freeze
Correct answer: A. expand
Explanation: Heating increases molecular motion, so most substances expand.
During a phase change (melting or boiling), temperature stays constant while heat is absorbed entirely as latent heat (Q=mL); temperature only rises again once the substance is fully in its new phase.
Concept context
Temperature scales, thermal expansion, calorimetry, and the three modes of heat transfer including radiation laws.