What is hemoglobin?

Which factors in the tissues favor the dissociation of oxygen from oxyhaemoglobin?

How many molecules of $O_2$ can one molecule of hemoglobin carry?

Select $(1)$ and $(2)$ from the given options for the reaction: $Hb + O_2 \rightleftharpoons HbO_2$

Which of the following major ions in the blood plays an important role in the transport of $CO_2$?

$CO_{2}$ diffuses into ...$A$... and forms $HCO_{3}^{-}$ and $H^{+}$. At the ...$B$... site where $pCO_{2}$ is low, the reaction proceeds in the opposite direction.
Thus, $CO_{2}$ is trapped as ...$C$... at the tissue level and transported to alveoli is released out as ...$D$...
Select the right choice for $A, B, C$ and $D$ to complete the given $NCERT$ statement.