The pH value is calculated mathematically as the

Correct Answer: D

Rationale: The pH value is the negative log of the hydrogen ion (H⁺) concentration (D), defined as pH = -log[H⁺], measuring acidity (e.g., pH 7 = 10⁻⁷ M H⁺). Option A (log[OH⁻]) and B (-log[OH⁻]) relate to pOH, not pH. Option C (log[H⁺]) omits the negative, yielding incorrect values. Option E (original) about ratios is unrelated. This logarithmic scale, rooted in the water dissociation constant (pH + pOH = 14), quantifies acidity impacting drug ionization (e.g., weak acids in stomach), a cornerstone of pharmaceutical chemistry.

Correct Answer: C

Rationale: Pulverization by intervention (C) is typically used to mill camphor, adding a volatile solvent (e.g., alcohol) to reduce it to a fine powder, then evaporating the solvent, overcoming camphor's waxy nature. Trituration (A) grinds without solvent, less effective here. Levigation (B) uses a liquid to make a paste, not ideal for camphor. Geometric dilution (D) mixes powders, not mills. Attrition (original E) is mechanical grinding, less specific. This method ensures uniformity for incorporation into ointments or inhalants, leveraging camphor's volatility for pharmaceutical use.

Correct Answer: C

Rationale: Cellulose acetate phthalate (C) is used to coat enteric tablets, dissolving above pH 6 (intestine), protecting drugs (e.g., aspirin) from gastric acid. Hydroxypropyl methyl cellulose (A) and carboxymethyl cellulose (B) are film-formers, not enteric-specific. No option D or original E exists. This pH-dependent coating delays release, reducing gastric irritation or degradation, critical for targeted delivery and efficacy in oral formulations, leveraging gastrointestinal pH gradients.

Correct Answer: D

Rationale: Simple diffusion (D) is the passage of drug molecules from high to low concentration, a passive process driven by the gradient (e.g., ethanol across membranes), requiring no energy. Active transport (A) uses energy against the gradient. Bioavailability (B) is the fraction reaching systemic circulation. Biopharmaceutics (C) studies formulation effects. Pinocytosis (original E) involves vesicular uptake. Diffusion's lipid solubility dependence governs most drug absorption, a fundamental principle in pharmacokinetics, impacting onset and distribution rates.

Correct Answer: B

Rationale: Nonlinear pharmacokinetics feature an elimination half-life (t_½) that increases as the dose increases (B), as elimination (e.g., via saturable enzymes) becomes zero-order (e.g., phenytoin), prolonging clearance at high doses. Option A is false; metabolite ratios change with saturation. Option C is incorrect; AUC rises disproportionately. Option D is wrong; high doses shift from first-order. Option E (original) about steady-state is first-order-specific. This saturation alters dosing (e.g., phenytoin monitoring), critical to avoid toxicity in nonlinear drugs.