Haldane effect is:

In the tissues, Hb unloads its oxygen and takes up CO2. CO2 enters red cells and combines with water to form H2CO3. CO2 + H2O - H2CO3 - H+ + HCO3- The H+ ions are taken up by the Hb (to form HHb); it is aided by the fact that deoxyhemoglobin is a better acceptor of H+. Also, deoxyhemoglobin more readily forms carbamino compounds. In lungs, the reactions are reversed. The inhaled O2 combines with Hb. Oxyhemoglobin is a better donor of H+; H+ is now released by Hb. H+ combines with HCO3- to form H2CO3. H2CO3 - CO2 + H2O. CO2 will be exhaled out. Thus, unloading of O2 in peripheral capillaries facilitates the loading of CO2, and oxygenation, in the lung-enhances the unloading of CO2. This has been termed "Haldane effect". Option A is correct.