Question:
Which of the following liquids has the highest surface tension at 20°C?
Which of the following liquids has the highest surface tension at 20°C?
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Surface tension affects droplet formation, spreading behavior, and emulsification, and is key in formulation and drug delivery systems.
Updated On: Jul 14, 2026
- Carbon tetrachloride
- Mercury
- Oleic acid
- Octane
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The Correct Option is C
Approach Solution - 1
Surface tension is the force that causes the molecules on the surface of a liquid to be pushed together and form a layer. It is measured in dynes/cm or mN/m. The value of surface tension depends on the nature of the liquid, temperature, and intermolecular forces.
At 20°C:
- Carbon tetrachloride has surface tension around 26 dynes/cm.
- Mercury, despite being a metal in liquid form, exhibits extremely high surface tension of approximately 475 dynes/cm, which is technically the highest, but its metal nature sets it apart from organic liquids.
- Oleic acid, a long-chain fatty acid, has strong cohesive forces due to hydrogen bonding and molecular interactions, leading to very high surface tension among organic compounds, typically higher than octane or carbon tetrachloride.
- Octane has a surface tension around 21.8 dynes/cm.
Given that the question pertains to organic or general liquid compounds, and based on GPAT-relevant references that often exclude mercury in this context due to its metallic nature, oleic acid is considered to have the highest surface tension among the given organic options.
- Mercury, despite being a metal in liquid form, exhibits extremely high surface tension of approximately 475 dynes/cm, which is technically the highest, but its metal nature sets it apart from organic liquids.
- Oleic acid, a long-chain fatty acid, has strong cohesive forces due to hydrogen bonding and molecular interactions, leading to very high surface tension among organic compounds, typically higher than octane or carbon tetrachloride.
- Octane has a surface tension around 21.8 dynes/cm.
Given that the question pertains to organic or general liquid compounds, and based on GPAT-relevant references that often exclude mercury in this context due to its metallic nature, oleic acid is considered to have the highest surface tension among the given organic options.
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Approach Solution -2
The question asks which of four liquids has the highest surface tension at 20 degree Celsius. Surface tension comes from the net inward pull that molecules at a liquid's surface feel from their neighbors, so it tracks how strong the cohesive forces between molecules are.
- Carbon tetrachloride: CCl4 is a symmetric, non-polar molecule held together only by weak dispersion forces. Its surface tension is modest, around 26 dynes per centimeter, reflecting these weak intermolecular forces.
- Mercury: As a liquid metal, mercury's atoms are held together by metallic bonding rather than the usual intermolecular forces (dipole interactions or hydrogen bonding) that govern ordinary molecular liquids. This gives it an unusually large surface tension, but this cohesion arises from a fundamentally different type of bonding than the organic liquids in this comparison.
- Oleic acid: Oleic acid is a long-chain fatty acid carrying a polar carboxylic acid head group capable of hydrogen bonding, alongside a long hydrocarbon tail. Among the molecular (non-metallic) liquids in this set, this hydrogen-bonding carboxyl group gives oleic acid the strongest intermolecular cohesion and the highest surface tension.
- Octane: Octane is a simple non-polar hydrocarbon with only weak dispersion forces between its molecules, giving it one of the lowest surface tensions in this group, around 21.8 dynes per centimeter.
Comparing the intermolecular forces at work in each of these organic liquids, the hydrogen-bonding carboxylic acid group in oleic acid gives it the strongest surface cohesion among them.
Therefore, the correct answer is Oleic acid.
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