Which of the following is not correctly matched?

Options

A. `{:("Column I","Column II"),("Photochemical smog","Warm dry climate"):}`
B. `{:("Column I","Column II"),("Photochemical smog","Contains" SO_(2)):}`
C. `{:("Column I","Column II"),("Classical smog","Cool humid climate"):}`
D. `{:("Column I","Column II"),("Classical smog","Reducing smog"):}`

Answer

To determine which of the following options is not correctly matched, we need to analyze the definitions and characteristics of photochemical smog and classical smog.

### Step-by-Step Solution:

1. **Understanding Photochemical Smog**:
- Photochemical smog is also referred to as "summer smog."
- It is formed primarily due to the high concentration of nitrogen dioxide (NO2) and other volatile organic compounds (VOCs).
- This type of smog is typically observed in urban areas, especially during warm, dry weather.

2. **Understanding Classical Smog**:
- Classical smog is often seen in cold, humid conditions, typically during winter.
- It is characterized by the presence of sulfur dioxide (SO2), carbon monoxide (CO), and particulate matter.
- Classical smog is known to be reducing in nature because substances like SO2 and CO can reduce other compounds.

3. **Analyzing the Options**:
- **Option A**: Photochemical smog matched with warm dry climate.
- This is correct as photochemical smog is indeed associated with warm, dry conditions.
- **Option B**: Photochemical smog matched with SO2.
- This is incorrect because photochemical smog primarily contains NO2 and VOCs, not SO2, which is associated with classical smog.
- **Option C**: Classical smog matched with cold humid climate.
- This is correct as classical smog occurs in cold and humid conditions.
- **Option D**: Classical smog matched with reducing smoke.
- This is correct since classical smog is reducing in nature.

4. **Conclusion**:
- The only option that is not correctly matched is **Option B**, which states that photochemical smog contains SO2.

### Final Answer:
**Option B** is not correctly matched.