Compound C is most likely to be an alcohol (option C) based on the information given.

Boiling points of compounds are influenced by intermolecular forces. The stronger the intermolecular forces, the higher the boiling point. There are three main types of intermolecular forces: London dispersion forces, dipole-dipole forces, and hydrogen bonding.

- London dispersion forces: These forces exist in all molecules and are caused by temporary fluctuations in electron distribution. They are the weakest intermolecular forces and increase with increasing molecular mass.
- Dipole-dipole forces: These forces occur between polar molecules and are caused by the attraction between the positive end of one molecule and the negative end of another. They are stronger than London dispersion forces.
- Hydrogen bonding: This is a specific type of dipole-dipole interaction that occurs between a hydrogen atom bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) and another electronegative atom. Hydrogen bonding is the strongest intermolecular force.

Based on the information given, compounds A, B, C, and D have similar molecular masses. This suggests that they may have similar London dispersion forces.

However, compound C has the highest boiling point among the four compounds. This indicates that compound C has stronger intermolecular forces compared to the other compounds. Since compounds A, B, C, and D have similar molecular masses, the difference in boiling points is likely due to the presence of additional intermolecular forces such as dipole-dipole forces or hydrogen bonding.

Alcohols are known to exhibit hydrogen bonding due to the presence of an -OH group. Hydrogen bonding is a strong intermolecular force and can significantly increase the boiling point of a compound. Therefore, compound C is most likely an alcohol.

It is important to note that without additional information about the structures and functional groups of the compounds, this conclusion is based on the given information and general trends in intermolecular forces.