Which factor in tissues favours the formation of $HCO_{3}^{-}$ and $H^{+}$ ions in the blood?

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.

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

The major fraction of $CO_2$ released during cellular respiration is transported by the blood to the lung capillaries as:

Each haemoglobin molecule can carry a maximum of

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