Which statement about ion trapping is correct?

• A. Weak acids trapped in the stomach due to acidity
• B. Weak bases trapped in the small intestine due to alkaline pH
• C. Ion trapping does not influence absorption
• D. Weak bases are trapped in the stomach due to the acidic environment

Answer: (D)

Ion trapping relies on pH-dependent ionization: only the nonionized form easily crosses membranes, while the ionized form is stuck in the compartment where the pH favors ionization. In the acidic stomach, weak bases become protonated to form charged species, which cannot cross the gastric lining and thus are trapped there. This trapping in the acidic environment reduces their absorption. By contrast, weak acids become more ionized in basic environments (like the intestine), leading to trapping there, not in the stomach. An alkaline pH would favor the uncharged form of a weak base, promoting absorption rather than trapping. Since ion trapping does influence absorption, the statement that weak bases are trapped in the stomach due to the acidic environment is the best description.