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Question:
Which of the following has the highest surface tension?
A)Water
B)Soap in water
C)Detergent in water
D)Glycerol in water


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Last updated date: 21st Apr 2024
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Answer
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Hint: Surface tension is basically the tendency of the fluid surfaces to shrink into minimum surface area possible. It is the phenomenon that occurs when the surface of a liquid is in contact with another phase. Moreover, the liquids tend to acquire the least surface area possible.

Complete step by step answer:
Surface tension is defined as the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which further tends to minimize the surface area. The forces behind the origin of surface tension are cohesive and adhesive forces.
Moreover, liquids tend to acquire the least surface tension. The intermolecular forces such as Vander Waals forces draw the liquid particles together. It is basically the ratio of the surface force F to the length L. It can mathematically be expressed as:
 $T = \dfrac{F}{L}$
Where, T is the surface tension of the liquid
F is the force per unit length
L is the length in which the force acts.
Now, the sparingly soluble salts and surface active substances decrease the surface tension of the liquid. However, the fairly soluble solutes increase the surface tension of the liquid. So, among the given options, Glycerol in water has the highest surface tension because glycerol has more hydrogen bonds formed per molecule.
Now, in the rest of the cases, the surface tension of soap in water and detergent in water is lower than the surface tension of pure water.
Hence, option D is correct.

Note: Some of the examples of surface tension are insects walking on water, floating of a needle on the surface of water, cleaning of clothes by soaps and detergents and washing with cold water etc. Moreover, the SI unit of surface tension is Newton per meter.