Which of the following gases forms carboxyhaemoglobin ?

Question

Accepted Answer

Carboxyhaemoglobin is a compound formed when carbon monoxide (CO) binds with hemoglobin in the blood. Here is a detailed explanation of why Option 1 is correct and why the other options are incorrect:

1. **Option 1: CO (Carbon Monoxide)**
   - Carbon monoxide is a colorless, odorless gas that can bind with hemoglobin to form carboxyhaemoglobin. This binding is much stronger than the binding of oxygen to hemoglobin, which means that even small amounts of carbon monoxide can significantly reduce the blood's ability to carry oxygen. This is why carbon monoxide is so dangerous and can lead to carbon monoxide poisoning. The formation of carboxyhaemoglobin is a key reason why exposure to carbon monoxide is hazardous to health.

2. **Option 2: $CO_{2}$ (Carbon Dioxide)**
   - Carbon dioxide does not form carboxyhaemoglobin. Instead, it is transported in the blood in three main forms: dissolved in plasma, chemically bound to hemoglobin as carbaminohemoglobin, and as bicarbonate ions. While carbon dioxide does interact with hemoglobin, it does not form carboxyhaemoglobin.

3. **Option 3: $CH_{4}$ (Methane)**
   - Methane is a simple hydrocarbon and does not interact with hemoglobin to form any compound similar to carboxyhaemoglobin. Methane is primarily a greenhouse gas and does not have a direct effect on hemoglobin in the blood.

4. **Option 4: $O_{2}$ (Oxygen)**
   - Oxygen binds to hemoglobin to form oxyhemoglobin, not carboxyhaemoglobin. The binding of oxygen to hemoglobin is essential for the transport of oxygen from the lungs to the tissues. Oxygen does not form carboxyhaemoglobin; instead, it competes with carbon monoxide for binding sites on hemoglobin.

In conclusion, Option 1 (CO) is the correct answer because carbon monoxide is the specific gas that forms carboxyhaemoglobin by binding with hemoglobin, thereby reducing the blood's oxygen-carrying capacity. The other options do not form carboxyhaemoglobin and are therefore incorrect in this context.