Smog is formed when :

Options

A. water combines with `O_2`
B. `H_2` combines with O
C. water combines with `SO_2`
D. smoke combines with fog

Answer

**Step-by-Step Solution:**

1. **Understanding Smog**: Smog is a type of air pollution that is a mixture of smoke and fog. It typically occurs in urban areas where there are high levels of pollution.

2. **Components of Smog**: Smog contains both primary and secondary pollutants. Primary pollutants include particulate matter such as dust and pollen, while secondary pollutants include nitrogen oxides and sulfur oxides.

3. **Formation of Smog**: The formation of smog is primarily associated with the combination of fog (which consists of tiny water droplets in the air) and air pollutants.

4. **Analyzing the Options**:
- Option A: Water combines with oxygen to form hydrogen peroxide (H2O2) - not related to smog.
- Option B: Hydrogen (H2) combines with oxygen to form water - not related to smog.
- Option C: Water combines with hydrogen peroxide to form sulfurous acid (H2SO3) - not related to smog.
- Option D: Smog combines with fog to form smog - this is the correct option.

5. **Conclusion**: The correct answer is that smog is formed when smog combines with fog.

**Final Answer**: Smog is formed when smog combines with fog (Option D).

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