A colourless, nonirritant , highly toxic gas that impairs respiration is

Options

A. `SO_(2)`
B. `NO_(2)`
C. `CO_(2)`
D. CO.

Answer

To solve the question "A colourless, nonirritant, highly toxic gas that impairs respiration is," we can follow these steps:

### Step 1: Identify the characteristics of the gas
The question describes a gas that is:
- Colourless
- Non-irritant
- Highly toxic
- Impairs respiration

### Step 2: Consider common gases that fit the description
We need to think about gases that are known to be colourless and non-irritant. Some gases to consider include:
- Carbon monoxide (CO)
- Carbon dioxide (CO2)
- Sulfur dioxide (SO2)
- Nitrogen dioxide (NO2)

### Step 3: Evaluate each gas against the criteria
- **Carbon monoxide (CO)**: It is colourless, non-irritant, highly toxic, and impairs respiration by binding to hemoglobin in the blood, preventing oxygen transport.
- **Carbon dioxide (CO2)**: While it is colourless and non-irritant, it is not highly toxic in normal concentrations and does not impair respiration in the same way as CO.
- **Sulfur dioxide (SO2)**: This gas is irritant and can cause respiratory issues, so it does not fit the criteria.
- **Nitrogen dioxide (NO2)**: This gas is also an irritant and can cause respiratory problems, making it an incorrect option.

### Step 4: Conclude with the correct answer
Based on the evaluation, the gas that fits all the criteria of being colourless, non-irritant, highly toxic, and impairing respiration is **carbon monoxide (CO)**.

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

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