Haemoglobin has highest affinity of which of the following gases ?

Options

A. Carbon monoxide
B. Carbon dioxide
C. Oxygen
D. Nitrogen

Answer

To determine which gas has the highest affinity for hemoglobin, we can analyze the options provided:

1. **Carbon Monoxide (CO)**: Hemoglobin has a significantly high affinity for carbon monoxide, about 210 times greater than that for oxygen. When hemoglobin binds with carbon monoxide, it forms carboxyhemoglobin, which can be dangerous as it prevents the transport of oxygen in the blood.

2. **Carbon Dioxide (CO2)**: While hemoglobin does bind to carbon dioxide, its affinity is much lower compared to carbon monoxide. Hemoglobin carries carbon dioxide in the form of carbaminohemoglobin, but it does not have the same high affinity as it does for carbon monoxide.

3. **Oxygen (O2)**: Hemoglobin's primary function is to transport oxygen from the lungs to the tissues. It has a high affinity for oxygen, but it is still lower than that for carbon monoxide.

4. **Nitrogen (N2)**: Hemoglobin does not have a significant affinity for nitrogen as it is an inert gas and does not participate in gas exchange in the body.

Based on this analysis, the gas with the highest affinity for hemoglobin is:

**Answer**: Carbon Monoxide (CO)

### Step-by-Step Solution:
1. **Identify the gases listed**: The options are Carbon Monoxide, Carbon Dioxide, Oxygen, and Nitrogen.

2. **Evaluate the affinity of hemoglobin for each gas**:
- Carbon Monoxide: Extremely high affinity (210 times greater than oxygen).
- Carbon Dioxide: Lower affinity compared to carbon monoxide.
- Oxygen: High affinity, but less than carbon monoxide.
- Nitrogen: Minimal to no affinity.

3. **Determine the gas with the highest affinity**: Based on the evaluations, Carbon Monoxide has the highest affinity for hemoglobin.

4. **Conclude with the correct answer**: The correct answer is Carbon Monoxide (CO).