Final answer:
The substance with the lowest surface tension among the choices is acetone ((CH₃)₂CO) because it only has dipole-dipole interactions, which are weaker than the hydrogen bonds and van der Waals forces found in the other substances. option a is correct.
Step-by-step explanation:
The substance with the lowest surface tension among the given options would be (CH3)2CO, which is acetone. Surface tension is largely influenced by intermolecular forces: the stronger the intermolecular forces, the higher the surface tension. Hydrogen bonds are the strongest intermolecular forces among those listed, which rules out water (H2O) that has very strong hydrogen bonding.
The alcohols, CH3OH and linear alkanes such as CH3CH2CH2CH3 (butane) and C6H14 (hexane), have weaker hydrogen bonding and van der Waals forces respectively, but still stronger than the dipole-dipole interactions present in acetone. As a result, acetone, due to its weaker dipole-dipole interactions and absence of hydrogen bonds, would have the lowest surface tension.