Final answer:
o-Chlorophenol can be separated from the other compounds using an aqueous KOH solution due to its acidic property, reacting with KOH to become water-soluble and moving from the DCM organic phase to the aqueous phase.
Step-by-step explanation:
The student's query involves a question of separation of compounds using solvent extraction with an aqueous potassium hydroxide (KOH) solution. Among the compounds listed - benzonitrile, o-chlorophenol, hexanone, butanal, and tert-butyl methyl ether - o-chlorophenol is the one that could be separated from the others using a KOH solution. The reason for this is o-chlorophenol's acidic property, which allows it to react with KOH to form a water-soluble salt, thereby moving into the aqueous phase from the dichloromethane (DCM) organic phase. This difference in solubility based on reaction with a base is a key principle in separation techniques.