Correct Option: A

CO₂ from the respiratory tissues to the lungs is transported by the blood in 3 ways:
(i) In dissolved state or as a physical solution: Very small amount physically dissolved in plasma (7% i.e. @ 0.3 ml of CO₂ by each 100 ml of blood)
(ii) Bicarbonate ions: @ 70% (i.e. @ 2.5 ml per 100 ml of blood) CO₂ diffuses in plasma & then into RBCs where it (in the presence of carbonic anhydrase) combines with H₂O to form carbonic acid which is almost spontaneously dissociated into hydrogen ion & bicarbonate ions.
(iii) Carbaminohaemoglobin: @ 23% (i.e. @ 1 ml of CO₂ per 100 ml of blood) combines with haemoglobin forming an unstable compound.