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Water may be one of the most abundant compounds on Earth, but it is also the most mysterious. Like most liquids, it becomes denser as it cools. But unlike them, it reaches a state of maximum density at 4 degrees Celsius, then decreases in density as it freezes.

In solid form, it is even less dense, the major reason why standard ice floats on water. This is one reason life on Earth flourished. If ice were denser than water, lakes and oceans would freeze solid from the bottom up, preventing life from happening in the way we know it.

A current unsolved mystery about water is known as the Mpemba Effect. The phenomenon is named after a Tanzanian student who in 1963 observed that hot ice cream mix freezes faster than cold. These same observation about the rate at which water freezes were also made by classical scientists such as Aristotle, Bacon, and Descartes. Mpemba published a short article announcing his ideas, but he had no experimental evidence to back up the thoughts.

A discrepant event is an idea that seems to defy logical thinking.

Which statement best describes the discrepant event that defines the Mpemba Effect?


Water should reach its maximum density at 4 degrees Celsius, not when it freezes as it normally does.


It should be easier to freeze cold water than warm water because cold water starts at a lower temperature.


Water should become less dense as it cools, not more dense as it always does.


’Bodies of water should freeze from the top down, not the bottom up, due to the high density of ice.

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