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Why are aquatic plants and animals able to survive in cold regions even when the atmospheric temperature falls below 0 °C?
AWater at 0 °C is densest and sinks to the bottom first
BWater at 4 °C is densest and sinks, so ice forms only on top
CIce is denser than water and sinks, warming the bottom
DWater never freezes in deep lakes at any temperature
Answer & Solution
Correct answer: B. Water at 4 °C is densest and sinks, so ice forms only on top
1. Water has maximum density at 4 °C due to its anomalous behaviour.
2. The densest 4 °C water sinks to the bottom, keeping it liquid.
3. Colder, less dense water rises and freezes only as a top layer of ice.
4. Ice is actually less dense than water, so it floats; hence the sinking-ice option is wrong.
_Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 5 "Heat", p.74_
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