Q. 335.0( 1 Vote )

Give reasons:

(i) Lakes freeze from top towards bottom.

(ii) Ice floats on water.

Answer :

(i) As we know that, , thus for a substance with lower density, its mass is also less. The density of ice is less than water. Cold water starts expanding, and becomes less dense than what it should be when temperature drops to 4°C. As a result cold water being less dense, floats on to the surface and when it comes to the chilly freezing weather conditions outside, it gets frozen.

(ii) Since water expands on freezing, so the volume of ice for the same mass of water is more than water. In other words, density of ice is lower than water and hence ice floats on water.

As , thus for a substance with lower density, its mass is also less.

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