Understanding the Question:
The question asks which of four listed metabolic reactions is a Phase II reaction.
Key Concept:
Phase I reactions modify an existing functional group on the drug (oxidation, reduction, hydrolysis), while Phase II reactions attach a small conjugating molecule onto the drug to raise its water solubility for excretion.
Checking Each Option:
Reduction and oxidation both modify an existing functional group on the molecule, placing them in Phase I.
Hydrolysis breaks a bond to expose a functional group rather than attaching anything new, also a Phase I reaction.
Acetylation transfers an acetyl group from acetyl coenzyme A onto an amine or hydroxyl group on the drug, which is a true conjugation reaction.
Final Answer:
Acetylation is the Phase II metabolism reaction among the four listed.