A very fine powdered chemical is defined as one that

Correct Answer: B

Rationale: A very fine powder completely passes through a #120 sieve (B), with mesh size ~125 μm, per USP standards, ensuring small, uniform particles for rapid dissolution (e.g., in suspensions). Option A (#80, ~180 μm) is fine, not very fine. Option C (#20, ~850 μm) is coarse. Option D describes a fine powder range. Option E (original) is coarser still. This fineness enhances bioavailability and mixing, critical in formulations where particle size affects absorption rates, like oral powders or inhalants.

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.

Correct Answer: A

Rationale: Nucleotides (A) are the building blocks of nucleic acids (DNA/RNA), comprising a sugar, phosphate, and base (e.g., ATP), polymerized via phosphodiester bonds. Nucleosides (B) lack phosphate. Monosaccharides (C) build carbohydrates. Purines (D) and amino acids (original E) are components, not full units. Nucleotides' role in genetic material and energy (e.g., GTP) underpins antiviral drugs (e.g., acyclovir), targeting replication, a critical biochemical and pharmacological concept.