Which one of the following is not a property of classical smog?

Options

A. Occurs at low temperature
B. Secondary pollutant play significant role
C. Contains `SO_(2)`
D. Dark brown coloured

Answer

To solve the question "Which one of the following is not a property of classical smog?", we will analyze the properties of classical smog and identify the incorrect statement.

### Step-by-Step Solution:

1. **Understanding Classical Smog**:
- Classical smog is a type of air pollution that typically occurs in cold and humid climates. It is characterized by a mixture of smoke and fog.

2. **Identifying Components**:
- The main components of classical smog include:
- Nitrogen oxides (NOx)
- Sulfur dioxide (SO2)
- Particulate matter
- These components are primarily pollutants that contribute to the formation of smog.

3. **Physical Appearance**:
- Classical smog has a dark brown haze-like appearance, which is a result of the pollutants present.

4. **Temperature Conditions**:
- Classical smog occurs at low temperatures, which is consistent with its formation in cold, humid environments.

5. **Primary vs. Secondary Pollutants**:
- It is important to distinguish between primary and secondary pollutants:
- **Primary Pollutants**: These are directly emitted from sources (e.g., NO2, SO2).
- **Secondary Pollutants**: These are formed through chemical reactions in the atmosphere (e.g., ozone, sulfuric acid).
- Classical smog is primarily composed of primary pollutants.

6. **Evaluating the Options**:
- Now, we will evaluate the given options to identify which one is not a property of classical smog:
- **Option A**: Occurs at low temperature - This is true.
- **Option B**: Secondary pollutant plays a significant role - This is false for classical smog as it is primarily composed of primary pollutants.
- **Option C**: Contains SO2 - This is true.
- **Option D**: Dark brown color - This is true.

7. **Conclusion**:
- The statement that is not a property of classical smog is **Option B**: "Secondary pollutant plays significant role".

### Final Answer:
**Option B**: Secondary pollutant plays significant role.

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