BCS Class III sits opposite to Class II: solubility is not the problem, but the drug struggles to cross the gut wall because it is too polar or too large to pass through the lipid membrane easily. Checking permeability behaviour across each option group identifies the right set.
- Acyclovir, Atenolol, Captopril: Acyclovir is a highly polar nucleoside analogue, atenolol is a hydrophilic beta blocker, and captopril is a small polar peptide-like molecule. All three dissolve completely in gastrointestinal fluid but rely on active transport or paracellular routes to cross the gut wall because passive diffusion through the lipid membrane is limited. This low permeability alongside full solubility is the hallmark of BCS Class III.
- Taxol, Ellagic acid, Aspirin: Taxol's main issue is the opposite one, very poor aqueous solubility despite decent membrane permeability, which is the BCS Class II pattern, so this group does not represent Class III as a set.
- Aspirin, Paracetamol, Amoxycillin: Aspirin and paracetamol are both soluble and readily permeable, the combination that defines BCS Class I, so high solubility with low permeability does not describe this trio.
- Chloroquine, Diltiazem, Metoprolol: These are lipophilic drugs that cross membranes efficiently, which again points toward high permeability rather than the restricted permeability that defines Class III.
Because acyclovir, atenolol, and captopril are all freely soluble yet poorly permeable across the gut membrane, the correct answer is Acyclovir, Atenolol, Captopril.