In blood,the majority of $CO_2$ is transported by which of the following?

Identify the wrong statement with reference to transport of oxygen.

Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?

$I.$ Increased partial pressure of $O_{2}$
$II.$ Increased partial pressure of $CO_{2}$
$III.$ Increased partial pressure of $H^{+}$
$IV.$ Decreased partial pressure of $O_{2}$
All the above situations favour the dissociation of oxyhaemoglobin except:

Oxyhaemoglobin is an unstable compound because

Exposure to carbon monoxide (from coal gas) is extremely dangerous and can kill a patient because