Question

Haemoglobin has maximum affinity for

• A. $\text{CO}_2$
• B. $\text{O}_2$
• C. CO
• D. $\text{H}^{+}$

Hint:

Danger fact: CO poisoning occurs because Hb binds CO 200x stronger than $\text{O}_2$.

Answer 1

The Correct Option is C

Concept: Haemoglobin (Hb) is a respiratory pigment present in red blood cells that transports oxygen. However, it can bind with other gases as well, and its affinity differs for each.
• Hb has normal affinity for $\text{O}_2$ to transport oxygen.
• Hb can bind with $\text{CO}_2$ (carbaminohaemoglobin) but with lower affinity.
• Hb has an extremely high affinity (about 200--250 times more than oxygen) for carbon monoxide (CO).

Step 1: Understand affinity concept.
Affinity refers to how strongly haemoglobin binds with a molecule.

Step 2: Compare affinities.
• $\text{O}_2$: Normal physiological binding
• $\text{CO}_2$: Weak binding
• CO: Very strong binding (forms carboxyhaemoglobin)
• $\text{H}^{+}$: Does not bind directly like gases

Step 3: Identify the highest affinity.
CO binds most strongly with haemoglobin, preventing oxygen transport.

Step 4: Conclusion.
Thus, haemoglobin has maximum affinity for carbon monoxide. Final Answer: Option (C)