Which one of the following is not a common component of photochemical smog-----

Options

A. Ozone
B. Acrolein
C. Peroxyacetyl nitrate
D. Chlorofluorocarbons

Answer

To determine which of the following is not a common component of photochemical smog, we need to analyze the options provided:

1. **Ozone (O3)**: Ozone is a significant component of photochemical smog. It is formed when sunlight reacts with pollutants such as volatile organic compounds (VOCs) and nitrogen oxides (NOx).

2. **Zirconial**: This term seems to be a misinterpretation or a typographical error, as "zirconial" is not a recognized component in the context of photochemical smog.

3. **Peroxyacetyl Nitrate (PAN)**: This is indeed a common component of photochemical smog. It is formed from the reaction of nitrogen oxides and volatile organic compounds in the presence of sunlight.

4. **Chlorofluorocarbon (CFC)**: CFCs are not a component of photochemical smog. Instead, they are known for their role in ozone layer depletion and are not typically involved in the formation of smog.

Based on this analysis, the option that is not a common component of photochemical smog is **Chlorofluorocarbon (CFC)**.

### Final Answer:
**Chlorofluorocarbon (CFC)** is not a common component of photochemical smog.

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