Answer: 4°C.
- A 4°C
- B 0°C
- C 100°C
- D −4°C
Correct answer: A. 4°C
Explanation: Owing to anomalous expansion, water is densest at about 4°C.
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.