Final answer:
b. In the form of bicarbonate
Most blood carbon dioxide is transported as bicarbonate ions, which act as a buffer and are reversible to facilitate CO₂ release in the lungs.
Step-by-step explanation:
Most carbon dioxide (CO₂) in the blood is transported in the form of bicarbonate. When CO₂ enters the blood, it reacts with water to form carbonic acid, which then quickly dissociates into hydrogen ions and bicarbonate ions. This reaction is reversible and is facilitated by an enzyme called carbonic anhydrase. The bicarbonate acts as a buffer and carries the majority of CO₂ to the lungs, where the reaction reverses to release CO₂ for exhalation. Therefore, the correct answer to the question is b. In the form of bicarbonate.