Final answer:
The correct order is phenol, p-xylene, anisole, naphthalene (option e). In RPLC, phenol elutes first because it's the least hydrophobic due to its polar hydroxyl group, followed by p-xylene, anisole, and then naphthalene, which is the most hydrophobic.
Step-by-step explanation:
In reverse-phase liquid chromatography (RPLC), the separation of compounds depends on their relative hydrophobicity. Compounds that are more hydrophobic will interact more with the non-polar stationary phase and elute later from the column. The stationary phase typically consists of a silica-based material coated with alkane chains, making it non-polar.
The compounds in question—p-xylene, anisole, naphthalene, and phenol—all differ in their hydrophobic character. Phenol, with its polar hydroxyl group, is the least hydrophobic and will elute first from the column. Naphthalene and p-xylene are both non-polar, but naphthalene is a larger molecule with a greater surface area, making it more hydrophobic than p-xylene. Anisole is less hydrophobic than naphthalene, but more so than p-xylene because of its methoxy group, which is less polar than the hydroxyl group but adds to the molecule's overall size and hydrophobicity.
Therefore, the correct elution order from most hydrophilic to most hydrophobic is: phenol, p-xylene, anisole, naphthalene. This corresponds to option e.