CO is absorbed by haemoglobin. Give reasons

Explanation

**Step-by-Step Solution:**

1. **Understanding Carbon Monoxide (CO):**
- Carbon monoxide (CO) is a colorless, odorless gas that is produced by the incomplete combustion of carbon-containing fuels.

2. **Interaction with Hemoglobin:**
- Hemoglobin is a protein found in red blood cells that is responsible for transporting oxygen from the lungs to the rest of the body.

3. **Formation of a Stable Complex:**
- When carbon monoxide enters the bloodstream, it binds to hemoglobin to form a stable complex known as carboxyhemoglobin. This binding is significantly stronger than the binding of oxygen to hemoglobin.

4. **Stability Comparison:**
- The affinity of carbon monoxide for hemoglobin is approximately 300 times greater than that of oxygen. This means that once CO binds to hemoglobin, it is very difficult for oxygen to displace it.

5. **Consequences of CO Binding:**
- The formation of the carboxyhemoglobin complex prevents hemoglobin from carrying oxygen. As a result, the body's tissues and organs become deprived of oxygen, leading to symptoms of oxygen deficiency.

6. **Health Implications:**
- The lack of oxygen can cause serious health issues, including unconsciousness and, in extreme cases, death. This is why carbon monoxide is considered a highly toxic gas.

**Final Answer:**
Carbon monoxide is absorbed by hemoglobin because it forms a stable complex (carboxyhemoglobin) that is approximately 300 times more stable than the oxygen-hemoglobin complex. This prevents hemoglobin from carrying oxygen, leading to oxygen deficiency, unconsciousness, and potentially death.

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