Answer: 5°C.
- A 0°C (some ice remains)
- B 5°C
- C 10°C
- D 15°C
Correct answer: B. 5°C
Explanation: Heat released by water cooling to 0°C = 200×4.2×25 = 21000 J. Heat needed to melt all the ice = 50×336 = 16800 J. Remaining heat = 4200 J raises the combined 250 g of water: 4200 = 250×4.2×ΔT, giving ΔT = 4°C, so final temperature is approximately 4 to 5°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.