Final answer:
option a.) H2O, because it experiences hydrogen bonding.
H2O has the highest boiling point among H2O, H2S, H2Se, and H2Te because of its ability to form hydrogen bonds, which are stronger than the London dispersion forces experienced by the other molecules.
Step-by-step explanation:
The molecule expected to have the highest boiling point is H2O (water).
This is because it forms hydrogen bonds, which are a type of extremely strong dipole-dipole interaction occurring when hydrogen is covalently bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine.
Water has a boiling point of 100°C, significantly higher than what would be expected based on its molar mass alone. This contrasts with other molecules such as H2S, H2Se, and H2Te which predominantly experience weaker London dispersion forces and do not participate in hydrogen bonding.
Consequently, these molecules have lower boiling points compared to water.
H2S, H2Se, and H2Te, have boiling points that increase with increasing molar mass due to the increasing strength of London dispersion forces.
However, despite the increase in mass, they still do not exceed the boiling point of water because, lacking hydrogen bonds, they possess weaker intermolecular forces overall.
Therefore, H2O's capacity to form hydrogen bonds is the main reason for its anomalously high boiling point, making option (a) the correct answer.