Answer
a. At high altitude, there are fewer oxygen molecules in the air we inhale.
b. The hemoglobin equilibrium shifts in the direction of the reactants, $O_2$ and $Hb$.
Work Step by Step
a. Due to the lower pressure, the same volume of air contains fewer oxygen molecules at high altitude.
b. With less oxygen in the air, the concentration of $O_2 $ in the reaction decreases, which makes the equilibrium shift in the direction of the reactants.
