Which factor causes the rightward shift of the oxygen dissociation curve?
Correct answer: A. an increase in PCO₂ partial pressure
An increase in PCO₂ partial pressure causes the rightward shift of the oxygen dissociation curve. This is because higher CO₂ levels lead to more H⁺ ions, which bind to hemoglobin and reduce its affinity for oxygen, facilitating easier release of oxygen to tissues.