Final answer:
The nurse's priority for the client is to apply oxygen therapy.
Step-by-step explanation:
The nurse's priority for the client whose ABG results show a pH of 7.31, PaCO2 of 50 mm Hg, and HCO3 of 25 mEq/L after experiencing an airway obstruction would be to apply oxygen therapy to the client. This is because the client's ABG results indicate a respiratory acidosis, with a lower than normal pH and higher PaCO2. Oxygen therapy can help to improve oxygenation and correct the acidosis.