Which of the following is not involved in the formation of photochemical smog ?

Options

A. NO
B. `O_(3)`
C. `C_(x)H_(y)`
D. `SO_(2)`

Answer

To solve the question of which substance is not involved in the formation of photochemical smog, we will follow these steps:

### Step 1: Understand Photochemical Smog
Photochemical smog is a type of air pollution that occurs when sunlight reacts with pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the atmosphere. This reaction leads to the formation of secondary pollutants, including ozone (O3) and nitrogen dioxide (NO2).

### Step 2: Identify the Components Involved
The main components involved in the formation of photochemical smog include:
- Nitrogen oxides (NOx)
- Hydrocarbons (CxHy)
- Sunlight (specifically ultraviolet rays)

### Step 3: Analyze the Given Options
The question provides options (A, B, C, D) and asks which one is not involved in the formation of photochemical smog. We need to identify the substances listed in the options.

### Step 4: Determine the Correct Answer
Among the common pollutants, sulfur dioxide (SO2) is typically associated with industrial pollution and is not a direct contributor to photochemical smog. Instead, it is more relevant to another type of smog known as "sulfurous smog." Therefore, if SO2 is one of the options, it would be the correct answer to the question.

### Step 5: Conclusion
Based on the analysis, we conclude that the substance that is not involved in the formation of photochemical smog is sulfur dioxide (SO2). Thus, the correct answer is option D.

### Final Answer
**Option D: SO2 is not involved in the formation of photochemical smog.**

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