Correct Option: A

Transport of CO₂ is much easier than O₂ because of the higher solubility of CO₂ than O₂. Almost 7% of CO₂ is transported in dissolved state in plasma. About 23% of the CO₂ is transported in the form of carbamino haemoglobin. 70% of CO₂ is transported in the form of bicarbonate ions. CO₂ reacts with water present in plasma.
Carbonic acid is unstable & gives H⁺ and HCO₃^–. H⁺ bind with haemoglobin to maintain the pH of blood while HCO₃^– remain in the blood and carries the CO₂ to lungs.