The equalitative sketches I, II and III given below show the variation of surface tension with molar concentration of three diferent aqueous solutions of `KCl, CH_(3)OH` and `CH_(3)(CH_(2))_(11)OSO_(3)^(-)Na^(+)` at room temperature.

The correct assignment of the sketches is

Options

A. I:KCl,II:`CH_(3)OH`,III:`CH_(3)(CH_(2))_(11)OSO_(3)^(-)Na^(+)`
B. I:`CH_(3)(CH_(2))_(11)OSO_(3)^(-)Na^(+)`,II:`CH_(3)OH`,III:KCl
C. I:KCl,II : `CH_(3)(CH_(2))_(11)OSO_(3)^(-)Na^(+)`,III: `CH_(3)OH`
D. I:`CH_(3)OH`,II: KCl , III : `CH_(3)(CH_(2))_(11)OSO_(3)^(-)Na^(+)`

Answer

D

Explanation

Impurities affect surface tension appreciably .It is observed that impurities which tend to concentrate on surface of liquids , compared to its bulk lower the surface tension .
Substances like detergents , soaps `(CH_(3)(CH_(2))_(11)SO_(3)^(-)Na^(+))`decreases the surface tension sharply .
Those like alcohoal `("e.g " . -CH_(3)OH,C_(2)H_(5)OH)` lower the surface tension slightly .This can also be related to the fact the `CH_(3)OH` has smaller dielectric constant . Dielectric constant is directly proportional to surface tension . So , on adding `CH_(3)OH` in water , overall dielectric constant decreases and surface tension decrease .
Inorganic impurities present in bulk of a liquid such as KCl tend to increase the surface tension of water .