Answer: 4°C.
- A 0°C
- B 4°C
- C 100°C
- D -4°C
Correct answer: B. 4°C
Explanation: Water shows anomalous expansion, contracting from 0°C to 4°C and expanding above 4°C, so its density is maximum at 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.