Which one of the following is colourless and highly toxic gas which reduces oxygen carrying capacity of blood?

Options

A. `SO_(2)`
B. CO
C. NO
D. `SO_(3)`

Answer

To solve the question about which gas is colorless, highly toxic, and reduces the oxygen-carrying capacity of blood, we can follow these steps:

### Step 1: Identify the Properties of the Gas
- The gas in question is described as colorless and highly toxic.
- It is also noted that it reduces the oxygen-carrying capacity of blood.

### Step 2: Consider Common Gases
- Common gases that are colorless and toxic include carbon monoxide (CO), carbon dioxide (CO2), and nitrogen dioxide (NO2).
- Among these, carbon dioxide is not highly toxic in normal concentrations, and nitrogen dioxide is not primarily known for affecting blood oxygen levels.

### Step 3: Analyze the Mechanism of Action
- Carbon monoxide is known to bind with hemoglobin in the blood.
- Hemoglobin normally binds with oxygen to form oxyhemoglobin, which is essential for transporting oxygen throughout the body.
- However, carbon monoxide has a much higher affinity for hemoglobin compared to oxygen.

### Step 4: Conclude the Answer
- When carbon monoxide binds with hemoglobin, it forms carboxyhemoglobin, which prevents hemoglobin from carrying oxygen.
- This results in a reduced oxygen-carrying capacity of the blood, leading to symptoms of poisoning.

### Final Answer
The gas that is colorless, highly toxic, and reduces the oxygen-carrying capacity of blood is **Carbon Monoxide (CO)**.

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