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

### Step-by-Step Solution:

1. **Identify the Properties of the Gas**:
We need to find a gas that is colorless, highly toxic, and has a significant effect on the blood's ability to carry oxygen.

2. **Consider Common Toxic Gases**:
Some common toxic gases include carbon monoxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2), and nitrogen dioxide (NO2). Among these, we need to identify which one meets all the criteria.

3. **Evaluate Carbon Monoxide (CO)**:
- Carbon monoxide is known to be a colorless gas.
- It is highly toxic and is primarily produced from the incomplete combustion of carbon-containing fuels.
- CO binds with hemoglobin in the blood to form carboxyhemoglobin, which significantly reduces the blood's ability to carry oxygen.

4. **Evaluate Other Gases**:
- Carbon dioxide (CO2) is colorless but is not highly toxic at normal concentrations and does not reduce the oxygen-carrying capacity of blood in the same way as CO.
- Sulfur dioxide (SO2) and nitrogen dioxide (NO2) are also toxic but are not colorless gases.

5. **Conclusion**:
Based on the evaluation, the gas that is colorless, highly toxic, and reduces the oxygen-carrying capacity of blood is **carbon monoxide (CO)**.

### Final Answer:
The correct answer is **carbon monoxide (CO)**.

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