Which of the following is the correct match?

Options

A. Classical smog - `NO_(2)`
B. Photochemical smog - `SO_(2)`
C. Greenhouse gas - `CH_(4)`
D. Both (1) & (3)

Answer

To solve the question of which of the following is the correct match, we will analyze each option step by step.

### Step 1: Analyze Option 1
- **Statement**: Classical smoke contains NO2.
- **Explanation**: Classical smoke is characterized by the presence of smoke, fog, and sulfur dioxide (SO2). It occurs in cool, humid climates and is reducing in nature. NO2 (nitrogen dioxide) is a component of photochemical smog, not classical smog.
- **Conclusion**: This option is **incorrect**.

### Step 2: Analyze Option 2
- **Statement**: Photochemical smog is SO2.
- **Explanation**: Photochemical smog occurs in dry, sunny climates and contains components such as ozone (O3), peroxyacetyl nitrate (PAN), acrolein, and nitrogen oxides (NO, NO2). SO2 (sulfur dioxide) is a component of classical smog, not photochemical smog.
- **Conclusion**: This option is **incorrect**.

### Step 3: Analyze Option 3
- **Statement**: Greenhouse gas CH4.
- **Explanation**: Methane (CH4) is indeed a greenhouse gas. Greenhouse gases trap heat in the atmosphere and contribute to the greenhouse effect. Other greenhouse gases include carbon dioxide (CO2), nitrous oxide (N2O), and ozone (O3).
- **Conclusion**: This option is **correct**.

### Step 4: Analyze Option 4
- **Statement**: Both first and third options are correct.
- **Explanation**: Since the first option is incorrect (classical smoke does not contain NO2), this statement cannot be true.
- **Conclusion**: This option is **incorrect**.

### Final Answer
The correct match is **Option 3: Greenhouse gas CH4**.

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