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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 researcher decides to complete an experiment to add to the body of knowledge concerning the Mpemba effect. He decides to obtain samples of pond water, lake water, and distilled water. The water samples are divided into a series of containers. Each container is the same size and shape and a graduated cylinder is used to place equal volumes of water into each vessel. The water in the containers is then heated or cooled to reach its prescribed starting temperature. Each container was then placed into a -30 degree Celsius freezer. The containers were inspected every five minutes and the time for the water to freeze to solid ice was recorded. Data was recorded in the following chart:

Type of Water: Distilled Pond Lake
Starting Temperature (Celsius) Time to Freeze (min) Time to Freeze (min) Time to Freeze (min)
5 70 63 64.5
10 70 62.5 64
15 69 60 61
20 65.4 59.6 60.4
25 62 57 59
30 58.7 54.5 58.2

Which statement most accurately reflects evidence that is found in the data table?


Lake water freezes more quickly than pond water.


Pond water forms ice crystals earlier than does distilled water or lake water.


Lake water contains impurities that allow ice crystals to form faster than pond or distilled water.


Distilled water, because of its purity, forms ice crystals more quickly than pond or lake water.

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