Correct Option
Carbon monoxide (CO) is a highly toxic gas. When inhaled, CO readily binds to haemoglobin (Hb) in red blood cells. Its affinity for haemoglobin is approximately 200-250 times greater than that of oxygen (O₂). This strong binding forms a stable compound called carboxyhaemoglobin (COHb), effectively preventing haemoglobin from binding with oxygen. Consequently, the oxygen-carrying capacity of the blood is severely reduced, leading to a diminished supply of oxygen to the body's tissues and organs, a condition known as hypoxia.
Incorrect Options
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Option (a) is incorrect. Carbon monoxide (CO) is not converted into carbon dioxide (CO₂) within the human body. Instead, it directly interferes with oxygen transport.
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Option (c) is incorrect. While CO binds to haemoglobin, it does not destroy the chemical structure of haemoglobin. It forms a reversible, albeit stable, complex (carboxyhaemoglobin) that occupies the oxygen-binding sites.
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Option (d) is incorrect. The primary effect of CO poisoning is on oxygen transport and delivery to tissues. While severe hypoxia can indirectly affect brain function, CO does not directly damage or adversely affect the respiratory control centre in the brain in the manner suggested.