The dissociation curve of haemoglobin is:

Haemoglobin $(Hb)$ transports oxygen from the lungs to tissues. The partial pressure of oxygen in the lungs is different from that in the tissues. Each $Hb$ can bind to up to four oxygen molecules. Suppose we have an equal number of $Hb$ and oxygen molecules,and all the oxygen molecules are in a bound form. Then,which of the following is true?

Which of the following has the highest affinity for hemoglobin?

If the concentration of $CO_2$ is higher,the oxygen dissociation curve will shift towards:

Which protein is essential for the transport of $O_2$?

Why does the blood not become acidic during the transport of $CO_2$?