Blood analysis of a patient reveals an unusually high quantity of carboxyhaemoglobin content. Which of the following conclusions is most likely to be correct?

Refer to the following statements:
$I$. Carbonic anhydrase is present in the erythrocytes.
$II$. In erythrocytes,the carbon dioxide combines with water and is transported.

People living at sea level have around $5 \; million$ $RBCs$ per cubic millimetre of their blood,whereas those living at an altitude of $5400 \; m$ have around $8 \; million$. This is because at high altitude:

At which level does the following reaction occur?
$H^+ + HCO_3^- \rightarrow H_2CO_3 \rightarrow H_2O + CO_2$

Carbonic anhydrase is found in

With reference to the oxyhaemoglobin dissociation curve,select the $INCORRECT$ statement/statements.
$I$. $100\%$ saturation is very common.
$II$. $95-97\%$ saturation takes place at $ppO_2 = 100 \text{ mm Hg}$ in alveoli.
$III$. At $30 \text{ mm Hg}$ of $ppO_2$,only $50\%$ saturation can be maintained.
$IV$. The oxyhaemoglobin dissociation curve is $J$-shaped.
Select the correct option.