Question

For which of the following gas, Haemoglobin has the maximum affinity?

• A. Oxygen $\left(O_2\right)$
• B. Carbon dioxide $\left(C{O}_2\right)$
• C. Carbon monoxide $\left(CO\right)$
• D. Hydrogen $\left(H_2\right)$

Answer 1

The correct option is C

Carbon monoxide $\left(CO\right)$

Carbon monoxide $CO$ binds with haemoglobin 200 times faster than even oxygen binds with haemoglobin. So haemoglobin has maximum affinity for CO. Moreover, haemoglobin combines with carbon monoxide to form carboxyhaemoglobin. So carbon monoxide reduces oxygen carrying capacity of haemoglobin by amount equivalent to amount of haemoglobin converted to carboxyhaemoglobin.