The toxic effect of carbon monoxide is due to its greater affinity for haemoglobin as compared to oxygen approximately by:

Explanation

Carbon monoxide is produced due to incomplete combustion, metallurgical operations and naturally by plants as well as animals. Carbon monoxide has 200 times more affinity to hemoglobin as compared to oxygen. Carbon monoxide combines with hemoglobin of blood and forms a stable compound called carboxyhemoglobin. At 50 ppm, CO converts 7.5% of hemoglobin into carboxy­ hemoglobin within 8 hours. It impairs oxygen transport resulting in headache, decreased vision, cardiovascular malfunction and asphyxial.