gs1medium
The surface of a lake is frozen in severe winter, but the water at its bottom is still liquid. What is the reason?
- A.Ice is a bad conductor of heat
- B.Since the surface of the lake is at the same temperature as the air, no heat is lost
- C.The density of water is maximum at 4°C
- D.None of the statements (a), B. and C. given above is correct.
▶ Answer & Explanation
Correct answer: C. The density of water is maximum at 4°C
Water exhibits anomalous expansion. Unlike most substances, water expands when cooled below 4°C. Its maximum density occurs at 4°C. As the surface cools, it reaches 4°C and becomes denser, sinking. Water below 4°C is less dense and floats, eventually freezing. This layered density prevents the entire water body from freezing, allowing aquatic life to survive at the bottom.
Source: UPSC gs1 2011