Atmosphere of big cities is polluted most by

Options

A. automobile exhausts
B. pesticide residue
C. household waste
D. radioactive fall-out

Explanation

### Step-by-Step Solution:

1. **Identify the Options**: The question provides four options:
- Automobile exhaust
- Pesticide residue
- Household waste
- Radiative fallout

2. **Analyze Each Option**:
- **Automobile Exhaust**: This is a significant source of air pollution in urban areas. It contains harmful pollutants such as carbon monoxide, nitrogen oxides, sulfur dioxide, and particulate matter.
- **Pesticide Residue**: While pesticides can contribute to pollution, they primarily affect water and soil rather than the atmosphere directly.
- **Household Waste**: This typically leads to soil and water pollution, not directly to atmospheric pollution.
- **Radiative Fallout**: This refers to radioactive materials that can contaminate the environment, but it is not a primary source of air pollution in cities.

3. **Determine the Major Pollutant**: Given that automobile exhaust is directly linked to air quality and is prevalent in big cities due to high vehicle usage, it is the most significant contributor to atmospheric pollution in urban areas.

4. **Conclusion**: Based on the analysis, the atmosphere of big cities is polluted most by **automobile exhaust**.

### Final Answer:
The atmosphere of big cities is polluted most by **automobile exhaust**.

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