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 determine which property is not associated with classical smog, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Classical Smog**:
- Classical smog is a type of air pollution that typically occurs in cold and humid conditions. It is formed from the mixture of smoke and fog.

2. **Analyzing the Properties**:
- **Property 1: Occurs at low temperature**:
- Classical smog is known to occur in cold and humid conditions. Therefore, this property is true for classical smog.

- **Property 2: Secondary pollutant plays a significant role**:
- Classical smog primarily consists of primary pollutants like sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter. Secondary pollutants, such as ozone (O3), are more relevant to photochemical smog. Thus, this property is false for classical smog and is our potential answer.

- **Property 3: Contains SO2**:
- SO2 is a primary pollutant found in classical smog. Therefore, this property is true for classical smog.

- **Property 4: Dark brown color**:
- Classical smog can appear dark due to the presence of pollutants like SO2, nitrogen oxides (NOx), and particulate matter. This property is also true for classical smog.

3. **Conclusion**:
- The only property that does not apply to classical smog is "secondary pollutant plays a significant role." Therefore, this is the correct answer to the question.

### Final Answer:
The property that is not associated with classical smog is: **"Secondary pollutant plays significant role."**

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