Correct option is B
The correct answer is (b) Both A and R are true but R is not the correct explanation of A.
1. Assertion A:
· True. Glacial lakes get stratified during winters due to the formation of different temperature layers, with colder water near the surface and denser water below. The topmost layer often freezes, while deeper layers remain unfrozen.
2. Reason R:
· True. Water has its maximum density at 4°C. This is a unique physical property where water at 4°C sinks because it is denser than water at other temperatures.
3. Why R is Not the Correct Explanation of A:
· Although both statements are true, the stratification of glacial lakes in winter is primarily due to the formation of ice and the difference in water temperatures rather than the fact that water has maximum density at 4°C. The maximum density property of water influences stratification, but it is not the sole reason for stratification in glacial lakes.
Information Booster 1. Stratification in Winter:
· In glacial lakes, the surface water cools and freezes, while the deeper water remains liquid and typically at 4°C due to its maximum density.
2. Water’s Density Property:
· Water is most dense at 4°C, which allows the bottom layers of lakes to stay at this temperature even when the surface freezes.
3. Lake Layers in Winter:
· Top Layer: Ice (0°C)
· Middle Layer: Cold water (0°C to 4°C)
· Bottom Layer: 4°C water (densest)
4. Why Ice Floats:
· Ice is less dense than liquid water, which prevents lakes from freezing solid and protects aquatic life.
Additional Knowledge · Thermal Stratification:
· The layering of water in lakes based on temperature differences.
· Turnover:
· Mixing of lake water in spring and fall due to temperature equalization.
· Density Anomaly of Water:
· Unlike most substances, water expands when it freezes, making ice less dense than liquid water.
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