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Correct Answer: 4°c
the correct answer to the question regarding the temperature at the bottom of a frozen lake when the atmospheric temperature is -10°c is 4°c. this phenomenon can be explained by understanding the properties of water, particularly how its density varies with temperature.
water has a unique property where it reaches its maximum density at about 4°c. when water is cooled below this temperature, it starts to expand, becoming less dense. this is why ice, which is water at 0°c or below, floats on liquid water.
in the scenario of a lake during freezing conditions, the surface of the lake cools down first due to exposure to the cold air. as the surface water cools and its temperature drops below 4°c, it becomes less dense and remains on the surface. when the temperature of this surface water reaches 0°c, it freezes, forming a layer of ice.
beneath this ice layer, the water remains in liquid form because the densest water at 4°c sinks to the bottom. this stratification prevents the water below from freezing easily, as ice formation typically occurs at the surface where the water has direct exposure to the freezing air. thus, even though the air temperature is -10°c, the bottom of the lake maintains a temperature of around 4°c, where the water is at its densest and thus most stable in liquid form.
consequently, regardless of how cold the weather gets, as long as the lake is deep enough to allow for this thermal stratification, the temperature at the bottom of the lake will typically hover around 4°c, ensuring a stable environment for aquatic life that can survive the winter months.
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