In patients with COPD, retaining CO2 can lead to respiratory acidosis. What ABG result is indicative of such a condition?

pH 7.50, PCO2 35 mm Hg, HCO3 24 mEq/L

pH 7.40, PCO2 40 mm Hg, HCO3 24 mEq/L

pH 7.30, PCO2 50 mm Hg, HCO3 24 mEq/L

pH 7.35, PCO2 40 mm Hg, HCO3 22 mEq/L