MCQ
By a surface of a liquid we mean.
  • A
    $A$ geometrical plane like $x = 0$
  • B
    All molecules exposed to the atmosphere.
  • $A$ layer of thickness of the order of $10^{-8}m.$
  • D
    $A$ layer of thickness of the order of $10^{-4}m.$

Answer

Correct option: C.
$A$ layer of thickness of the order of $10^{-8}m.$
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 $1nm = 10^{-9}m$ so a diameter of $10$ to $15$ times would be of order$, 10 \times 10^{-9} = 10^{-8}m.$

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