The pollutants which come directly in the air from sources are called primary pollutes. Primary polluants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants ?

Options

A. `CO`
B. Hydrocarbon
C. Peroxyacetyl nitrate
D. `NO`

Answer

To determine which of the following belongs to secondary air pollutants, we first need to understand the definitions and examples of primary and secondary pollutants.

### Step-by-Step Solution:

1. **Understanding Primary Pollutants**:
- Primary pollutants are those that are emitted directly from a source into the air.
- Examples include oxides of nitrogen (NO, NO2, N2O), sulfur dioxide (SO2), carbon monoxide (CO), and carbon dioxide (CO2).

2. **Understanding Secondary Pollutants**:
- Secondary pollutants are not emitted directly. Instead, they form in the atmosphere through chemical reactions involving primary pollutants.
- Examples of secondary pollutants include ozone (O3), hydrogen peroxide (H2O2), nitric acid (HNO3), sulfuric acid (H2SO4), and peroxyacetyl nitrate (PAN).

3. **Identifying Secondary Pollutants**:
- From the list of examples, we can see that ozone, hydrogen peroxide, nitric acid, sulfuric acid, and peroxyacetyl nitrate are all secondary pollutants as they are formed from reactions involving primary pollutants.

4. **Conclusion**:
- Among the options provided, the only one that is a secondary air pollutant is peroxyacetyl nitrate (PAN).

### Final Answer:
The secondary air pollutant among the given options is **peroxyacetyl nitrate (PAN)**.

---