Excessive release of the pollutant carbon monoxide (CO) into the air may produce a condition in which oxygen supply in the human body decreases. What causes this condition?

Answer: (b) The inhaled CO has much higher affinity for hemoglobin as compared to oxygen

Haemoglobin binds CO about 200–250 times more strongly than oxygen, forming carboxyhaemoglobin — less oxygen reaches the tissues.

The idea

Haemoglobin in red blood cells carries oxygen from the lungs to the body. Carbon monoxide fits the same seat on haemoglobin and holds it more than 200 times more firmly. Once it sits there, oxygen cannot. The blood is full of haemoglobin but carries little oxygen.

CO is breathed in → Binds to haemoglobin → carboxyhaemoglobin → Oxygen cannot attach → Tissues are starved of oxygen → Headache, drowsiness, death

Why the others are wrong

(a) CO is not converted to CO₂ in the body.

(c) CO doesn’t destroy haemoglobin; it occupies it.

(d) The main effect is in the blood, not the brain’s respiratory centre.

The trap

(c) sounds dramatic, but the problem is blocking, not destruction.

Also know

Carbon monoxide has no colour or smell, so the victim gets no warning. It forms when fuel burns with too little air: a coal angithi or generator in a closed room, a running car in a shut garage. Treatment is fresh air and pure oxygen.