What should be the nature of blood for the efficient transport of $O_2$ and $CO_2$?

$CO$ is more toxic than $CO_2$ because:

The following statements refer to the transportation of gases. Read them carefully and choose the correct option containing the incorrect statements.
$(i)$ After leaving the lungs, each litre of blood contains about $20 \ ml$ of oxygen.
$(ii)$ When $PCO_2$ rises, the affinity of haemoglobin for oxygen is increased.
$(iii)$ Each litre of arterial blood contains about $4 \ ml$ of $CO_2$.
$(iv)$ The role of oxygen in the regulation of respiratory rhythm is quite significant.

How many oxygen molecules can one hemoglobin molecule carry?

Which is called Hamburger shift?

Carbon dioxide is transported in the blood to the lungs in the form of: