In presence of ADH, the reabsorption of water in collecting duct:

Correct Answer: C

Rationale: With ADH, water reabsorption in collecting duct is passive osmosis via aquaporins (e.g., medullary gradient). Active transport is Na not water. Cortical-only mislimits medullary too. All passive distinguishes it, key to ADH's osmotic drive, unlike active or partial errors.

Correct Answer: C

Rationale: Simultaneous respiratory (PCO₂ 68, high) and metabolic acidosis (HCO₃⁻ 13, low) match pH 6.90 severe drop (e.g., overdose hypoventilation, lactic acidosis). Uncompensated metabolic lacks PCO₂ rise partial. Uncompensated respiratory misses HCO₃⁻ drop sole. Renal compensation raises HCO₃⁻ not here. Dual acidosis distinguishes it, key to mixed disorder, unlike single or compensated states.

Correct Answer: A

Rationale: Urine forms via filtration (glomerulus), reabsorption (tubules), and secretion (tubules) not digestive or GI processes. This outlines nephron function, critical for waste removal, contrasting with unrelated mechanisms.

Correct Answer: A

Rationale: Normal urine pH is ~6.0 (slightly acidic) not neutral, alkaline, or strongly acidic (pathological). This defines typical acidity, critical for urinalysis, contrasting with abnormal ranges.

Correct Answer: C

Rationale: Normal urine output is 1-2 L/day not lower (oliguria) or higher (polyuria). This quantifies healthy production, critical for assessing function, contrasting with abnormal volumes.