It's difficult to definitively say which molecule is the *most* hydrophobic, as hydrophobicity is a relative property and can depend on the specific environment and conditions. However, some molecules are generally considered to be highly hydrophobic:

* Perfluorocarbons (PFCs): These are compounds containing only carbon and fluorine atoms. The high electronegativity of fluorine creates a very strong nonpolar bond with carbon, making PFCs extremely hydrophobic. Examples include perfluorooctane (C8F18) and perfluorodecalin (C10F18).

* Saturated hydrocarbons: These molecules are made up of only carbon and hydrogen atoms linked by single bonds. They lack polar groups and are therefore very hydrophobic. Examples include methane (CH4), ethane (C2H6), and hexane (C6H14).

* Aliphatic chains: Long chains of carbon and hydrogen atoms, common in fats and oils, are generally hydrophobic.

It's important to note that:

* Hydrophobicity is a spectrum: There isn't a clear line dividing molecules into "hydrophobic" and "hydrophilic." Instead, molecules exhibit a range of hydrophobicities.

* Hydrophobicity is context-dependent: The hydrophobicity of a molecule can be affected by factors such as the solvent it's in, the temperature, and the presence of other molecules.

So, while PFCs and saturated hydrocarbons are among the most hydrophobic molecules, it's not possible to declare a single "most hydrophobic" molecule without specifying the context.