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Question
By a surface of a liquid we mean
Options
a geometrical plane like x = 0
all molecules exposed to the atmosphere
a layer of thickness of the order of 10−8m
a layer of thickness of the order of 10−4m
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Solution
The surface of a liquid refers to the layer of molecules that have higher potential energy than the bulk of the liquid. This layer is typically 10 to 15 times the diameter of the molecule. Now, the size of an average molecule is around 1 nm = \[{10}^{- 9}\] m, so a diameter of 10 to 15 times would be of order \[10 \times {10}^{- 9} = {10}^{- 8}\] m .
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