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UPSC 2011: 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
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Not attemptedCorrect Answer: (c) The density of water is maximum at 4°C
Water attains maximum density at 4 °C; when surface water cools below this, it becomes lighter and remains on top, freezes and forms ice. The denser 4 °C water sinks, so the deeper layer stays liquid. Ice also insulates, but the decisive physical reason is the 4 °C density maximum. Options (a) and (b) are therefore incomplete/incorrect, making option (c) the only correct choice. ([upscprep.com](https://www.upscprep.com/upsc-prelims-2011-gs-question-paper-and-answer-key/))
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Frequently Asked Questions
What is the correct answer to this UPSC 2011 Science & Technology question?▼
The correct answer is option (c): The density of water is maximum at 4°C. Watch the detailed video explanation in our Sherlocking Prelims course on UnlockIAS.
Which year was this Physics question asked in UPSC Prelims?▼
This question was asked in UPSC CSE Prelims 2011, GS Paper 1, as Question 50. It falls under Science & Technology > Physics.
What is the difficulty level of this UPSC question?▼
This question is rated "easy". It tests basic recall and most well-prepared aspirants should answer it correctly.
How many UPSC Prelims questions have been asked from Physics?▼
UPSC has asked 104 questions from Physics (under Science & Technology) across multiple years. Visit the topic page to see the full list and year-wise trends.