Which of these gases when inhaled reduces the oxygen-carrying capacity of blood?

Options

A. Carbon dioxide
B. Sulphur dioxide
C. CFC
D. Carbon monoxide

Explanation

To solve the question "Which of these gases when inhaled reduces the oxygen-carrying capacity of blood?" we can follow these steps:

### Step 1: Identify the gases listed in the options.
The options given are:
- Carbon Dioxide
- Sulfur Dioxide
- CFC (Chlorofluorocarbon)
- Carbon Monoxide

### Step 2: Understand the function of hemoglobin in the blood.
Hemoglobin is a protein in red blood cells that binds to oxygen and carries it throughout the body. It is crucial for transporting oxygen from the lungs to the tissues.

### Step 3: Analyze the effects of each gas on hemoglobin.
- **Carbon Dioxide**: While it is a waste product of respiration, it does not significantly reduce the oxygen-carrying capacity of blood.
- **Sulfur Dioxide**: This gas can irritate the respiratory system but does not directly affect hemoglobin's ability to carry oxygen.
- **CFC (Chlorofluorocarbon)**: These are primarily used in refrigeration and aerosol propellants. They do not interact with hemoglobin.
- **Carbon Monoxide**: This gas has a very high affinity for hemoglobin, meaning it binds to hemoglobin more readily than oxygen does. When carbon monoxide is inhaled, it competes with oxygen for binding sites on hemoglobin, thus reducing the amount of oxygen that can be transported in the blood.

### Step 4: Conclude which gas is the correct answer.
Based on the analysis, carbon monoxide is the gas that, when inhaled, reduces the oxygen-carrying capacity of blood due to its higher affinity for hemoglobin compared to oxygen.

### Final Answer:
The gas that reduces the oxygen-carrying capacity of blood when inhaled is **Carbon Monoxide**.

---