What is the shape of the oxygen-hemoglobin dissociation curve?

Body tissues obtain $O_2$ from hemoglobin. The dissociation of oxyhemoglobin in the tissues is primarily caused by which of the following conditions?

Given below are two statements:
Statement $I$: The relationship between $HbO_2$ saturation and oxygen tension $(pO_2)$ is called the oxygen-dissociation curve.
Statement $II$: The oxygen dissociation curve shifts towards the right due to a decrease in $ppCO_2$ and a decrease in temperature.
In the light of the above statements,choose the most appropriate answer from the options given below.

The toxic effect of carbon monoxide is due to its greater affinity for haemoglobin as compared to oxygen by (approx.) (in $\times$)

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.

Name the enzymes $A$ and $B$ in the following equation:
$CO _2+ H _2 O \underset{B}{\stackrel{A}{\rightleftharpoons}} H _2 CO _3 \underset{B}{\stackrel{A}{\rightleftharpoons}} HCO _3^{-}+ H ^{+}$