Which one of the following is a secondary pollutant?

Options

A. CO
B. `O_(3)`
C. Pb
D. `CH_(4)`

Answer

To determine which of the following options is a secondary pollutant, we need to understand the definitions and characteristics of primary and secondary pollutants.

### Step 1: Define Primary and Secondary Pollutants
- **Primary Pollutants**: These are pollutants that are directly emitted into the atmosphere from a source. Examples include carbon monoxide (CO), sulfur dioxide (SO2), and particulate matter.
- **Secondary Pollutants**: These are not emitted directly. Instead, they form in the atmosphere through chemical reactions involving primary pollutants. An example is ozone (O3), which is formed from the reaction of sunlight with pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs).

### Step 2: Analyze the Options
- **A. CO (Carbon Monoxide)**: This is a primary pollutant produced from incomplete combustion of carbon-containing fuels.
- **B. O3 (Ozone)**: This is a secondary pollutant formed through photochemical reactions involving nitrogen oxides and other compounds in the presence of sunlight.
- **C. PB (Lead)**: This is a primary pollutant that can be emitted from industrial processes and vehicle emissions.
- **D. CH4 (Methane)**: This is also a primary pollutant emitted from natural sources and human activities like fossil fuel extraction.

### Step 3: Identify the Secondary Pollutant
From the analysis:
- CO, PB, and CH4 are all primary pollutants as they are emitted directly into the atmosphere.
- O3 is formed through reactions and is therefore classified as a secondary pollutant.

### Conclusion
The correct answer is **B. O3 (Ozone)**, as it is the only secondary pollutant among the options provided.

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