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Density of water varies with temperature. What are its consequences?

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Hint: It is known to us that density of water depends on temperature but the relation is not linear one. Also, it is known to us that density changes with temperature because of changing temperature, volume changes.

Complete step by step solution:
We know that density is the ratio of mass to volume. So, when temperature varies, the volume of liquid changes.
It is seen that when temperature increases, then volume also increases and since, volume is directly proportional to temperature. Therefore,on increasing the temperature of water from, density decreases.
Also, when water is cooled, it first contracts in volume like other liquids but below ${4^\circ }C$ it starts expanding and continues to do so till the temperature reaches ${0^\circ }C$, the point at which water freezes into ice and when ice is formed, density reduces.
Therefore, from above we can conclude that the main consequence of variation of density of water with temperature is that water has its highest density at ${4^\circ }C$. So, at low temperature in the ocean, top layer of water freezes into ice but the water below this layer will remain in liquid form which allows the existence of aquatic species even in cold regions.

Note: We should remember that the property of anomalous expansion of water enables marine life to exist in colder regions, because even when the water freezes on the top, it will still be liquid below the ice layer. Also the soft drink bottles are kept slightly empty in order to prevent the breaking of the bottle when water freezes.