UPSC CSE Prelims
Question 29
The surface of a lake is frozen in severe winter, but the water at its bottom is still liquid. What is the reason ?
View correct answer and explanation
Correct answer: C
Correct Option: C
Explanation: Water has its maximum density near 4°C, so this denser liquid sinks, while colder water and ice remain above, allowing deeper water to stay liquid.
Option-wise Analysis:
A: Incorrect - Ice insulation helps, but cannot by itself explain the vertical density stratification.
B: Incorrect - Lake surfaces can continue to lose heat; this claim is false.
C: Correct - maximum density at 4°C keeps relatively warm water at depth beneath surface ice.
D: Incorrect - One listed reason is correct, so “none” is wrong.