During the chloride shift, which of the following ions moves into the erythrocyte to maintain electrical neutrality as bicarbonate ions diffuse out?

Solution

1. Carbon dioxide reacts with water to form carbonic acid, which dissociates into $H^{+}$ and ${\text{HCO}}_3^{-}$.
2. To prevent accumulation of ${\text{HCO}}_3^{-}$ inside the erythrocyte, it is transported out into the plasma.
3. To maintain electrical neutrality, $C{l}^{-}$ ions move from the plasma into the erythrocyte.
4. Hence the answer is (C).