Rationale: A. PaCO2 50 mm Hg is correct because normal PaCO2 is 35–45 mm Hg, so a value above 45 mm Hg indicates hypercapnia, confirming that the lungs are retaining CO2. In acute respiratory acidosis, the elevated PaCO2 is the primary abnormality, and the pH decreases because renal compensation has not yet occurred. B. HCO3- 30 mEq/L is incorrect because normal bicarbonate is 22–26 mEq/L. Elevated bicarbonate occurs only in chronic or compensated respiratory acidosis when the kidneys retain HCO3- to buffer excess hydrogen ions. In acute cases, HCO3- is usually normal. C. pH 7.45 is incorrect because normal pH is 7.35–7.45, and respiratory acidosis is characterized by a pH below 7.35. A pH of 7.45 is alkalemic and would indicate respiratory alkalosis rather than acidosis. D. Potassium 3.3 mEq/L is incorrect because acute respiratory acidosis often causes hyperkalemia due to hydrogen ions shifting into cells in exchange for potassium. Hypokalemia is not characteristic of this condition.