Consider the following statements : Statement-I : Marine animals remain alive in winter and move near the bottom of lakes despite frozen water on the surface. Statement-II : The density of water is maximum at 4°C and water at the bottom of lakes remains warm in winter. Which one of the following is correct in respect of the above statements?
- A.Both Statement-I and Statement-II are correct and Statement-II explains Statement-I.
- B.Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I.
- C.Statement-I is correct, but Statement-II is not correct.
- D.Statement-I is not correct, but Statement-II is correct.
Correct answer
Explanation
The correct answer is A, both statements are correct and Statement-II explains Statement-I. Because water is densest at 4°C, the bottom of a lake stays liquid and relatively warm while the surface freezes, so aquatic animals survive there.
This is the anomalous expansion of water. As a lake cools, surface water sinks until the whole lake reaches about 4°C. Further cooling makes the surface water lighter, so it stays on top and turns to ice. Ice is a poor conductor of heat and floats, insulating the water below, which remains near 4°C through the winter. Fish and other animals simply move down to this layer.
B is wrong because Statement-II is the very reason Statement-I happens.
C is wrong because Statement-II is a correct property of water.
D is wrong because animals do survive under frozen lakes, so Statement-I is true.
Exam tip: water has maximum density at 4°C; ice floats and insulates the water beneath it.
Practice Questions
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- B.F is maximum when v and B are anti-parallel to each other.
- C.F is maximum when v and B are perpendicular to each other.
- D.The force F is independent of the angle between v and B.
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- A.Both the statements are individually true and Statement II is the correct explanation of Statement I
- B.Both the statements are individually true but Statement II is not the correct explanation of Statement I
- C.Statement I is true but Statement II is false
- D.Statement I is false but Statement II is true
Show answer
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