Answer: 25 C.
- A 30 °C
- B 40 °C
- C 25 °C
- D 22 °C
Correct answer: C. 25 °C
Explanation: 0.2 × 400 × (100 − T) = 0.3 × 4200 × (T − 20) gives T ≈ 25 °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.