Question

Which of the following combines with haemoglobin of the blood to form carboxyhemoglobin?
A. $CO$
B. $C{{O}_{2}}$
C. ${{N}_{2}}$
D. ${{O}_{2}}$

Answer 1

Hint: Oxygen and carbon monoxide gas can easily combine with haemoglobin of our blood. But the only difference is that the combination of oxygen with haemoglobin makes blood pure where the combination of carbon monoxide with haemoglobin makes blood impure.

Complete Step by Step Solution:
Haemoglobin is the major constituent of our blood. Haemoglobin contains the heme unit. It contains the only metal atom iron. In haemoglobin the iron atom exists in a $+2$ oxidation state. Haemoglobin contains a porphyrin ring where the iron atom is connected with the porphyrin ring through nitrogen atoms of the porphyrin ring.

Oxygen can combine with haemoglobin in a bent fashion called as oxy haemoglobin and increases the oxidation state of iron to $+3$. The combination of oxygen makes haemoglobin pure and supplies the oxygen to our blood.

Carbon monoxide can combine with the iron centre of the haemoglobin in a linear fashion called carboxyhemoglobin . The combination of carbon monoxide makes haemoglobin impure and causes many diseases.
Thus the correct option is $A$.

Note: Hemoglobin is essential for oxygen transport in our blood. The iron atom remains in $+2$ oxidation state and exist as high spin iron. When iron connects with oxygen atom in a bent fashion the oxidation state of iron changes to $+3$ and iron becomes low spin.