Of the following metals which one pollutes the air of a big city?

Options

A. Copper
B. Chromium
C. Lead
D. Cadmium

Explanation

To solve the question of which metal pollutes the air of a big city, we can follow these steps:

### Step 1: Identify the metals listed in the question
The metals given in the question are:
- A: Copper
- B: Chromium
- C: Lead
- D: Cadmium

### Step 2: Understand the pollution potential of each metal
Next, we need to evaluate the pollution potential of each metal:
- **Copper**: Generally not known to be a significant air pollutant.
- **Chromium**: Can be harmful in certain forms but is not a major contributor to air pollution in urban areas.
- **Lead**: Known for its harmful effects on health and is a significant air pollutant, especially from sources like vehicle emissions and industrial processes.
- **Cadmium**: Toxic and can cause pollution, but it is less common in the air compared to lead.

### Step 3: Determine which metal is primarily responsible for air pollution
From the evaluation, we find that:
- **Lead** is the metal that is primarily responsible for polluting the air in big cities due to its widespread use in fuels and industrial processes.

### Conclusion
Thus, the answer to the question is:
**C: Lead**

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