Based on the relation between the degree of ionization and the solubility of a weak acid, the drug aspirin (pKa 3.49) will be most soluble at

Correct Answer: D

Rationale: Aspirin (pKa 3.49) is most soluble at pH 4.0 (D). As a weak acid, its solubility increases when ionized (A⁻ form), per Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA]). At pH 4.0, pH > pKa, favoring ionization (log(0.51) ≈ 0.2, [A⁻] > [HA]), enhancing water solubility. At pH 1.0 (A), 2.0 (B), and 3.0 (C), pH < pKa, aspirin is mostly un-ionized (lipid-soluble), less soluble. pH 6.0 (original E) increases solubility further, but D is closest optimal. This pH-dependent solubility aids aspirin's absorption in the intestine (pH ~6), not stomach (pH ~2), guiding formulation strategies.

Correct Answer: A

Rationale: Divided powders are dispensed in individual-dose packets (A), pre-measured paper or foil packets (e.g., headache powders) ensuring accurate dosing and convenience. Bulk containers (B) suit undivided powders. Sifter-type containers (C) are for topical use, not oral doses. No option D or original E exists. This packaging protects hygroscopic or unstable drugs, enhancing patient compliance and stability, a traditional yet effective dispensing method in pharmacy practice.

Correct Answer: C

Rationale: Drugs are absorbed best from the duodenum (C) after oral administration, due to its large surface area (villi), neutral pH (~6-7), and long transit time, favoring ionization and dissolution (e.g., aspirin). Buccal (A) suits sublingual bypass. Stomach (B) has acidic pH, limiting weak acid absorption. Ileum (D) absorbs but less than duodenum. Rectum (original E) is for suppositories. This small intestinal dominance, post-gastric emptying, maximizes bioavailability, critical for oral drug design, though first-pass metabolism may reduce it.

Correct Answer: A

Rationale: The intensity of pharmacologic action depends most on the concentration of the drug at the receptor site (A), as receptor occupancy drives effect (e.g., acetylcholine at muscarinic receptors), per the law of mass action. Half-life (B) affects duration, not intensity. Onset time (C) reflects absorption, not effect strength. MTC (D) and MEC (original E) are plasma thresholds, not receptor levels. This receptor-centric principle, foundational to pharmacodynamics, links dose, distribution, and response, guiding therapeutic efficacy and titration.

Correct Answer: C

Rationale: The liver (C) has the greatest capacity to bio-transform drugs, via enzymes like CYP450 (e.g., oxidizing codeine to morphine), handling most metabolism due to its size and enzyme abundance. Brain (A) and kidney (B) have limited roles. Lung (D) metabolizes some (e.g., nicotine), less than liver. Skin (original E) is minimal. The liver's first-pass effect and phase I/II reactions (e.g., glucuronidation) detoxify and excrete drugs, central to pharmacokinetics, impacting bioavailability and clearance.