Chloride shift during CO2 transport in blood

Steps:

• CO2 diffuses from plasma into red blood cells (RBCs).
• Inside RBCs, CO2 + H2O forms H2CO3 via carbonic anhydrase, dissociating to H+ and HCO3- (with minor CO3^2- at high pH).
• HCO3- exits RBC into plasma via anion exchanger.
• Cl- enters RBC from plasma to balance charge.

Why B is correct:

• Matches the anion exchange: CO3- (minor form from HCO3- dissociation), H+ (from acid dissociation), HCO3- (exits to plasma), Cl- (enters RBC), per the Hamburger phenomenon definition.

Why the others are wrong:

• A: Swaps HCO3- and H+ roles, and includes irrelevant CO3- as 4; ignores Cl- exchange.
• C: Includes CO2 (gas diffusion, not ion) and wrong CO3- for 3; omits HCO3-.
• D: Reverses CO3- and HCO3- assignments, mismatching outflow direction.

Final answer: B