Correct the following statements by changing the underlined part of the sentence :
The surface of copper is covered by a green thin film due to the action of `ul("dry air")`

Explanation

To correct the statement "The surface of copper is covered by a green thin film due to the action of dry air," we need to replace "dry air" with the appropriate term that accurately describes the condition leading to the green film on copper.

### Step-by-Step Solution:

1. **Identify the Incorrect Part**: The phrase "dry air" is the part that needs correction. The green film on copper is not due to dry air.

2. **Understand the Cause of the Green Film**: The green film on copper is primarily due to the corrosion process, which occurs when copper reacts with moisture and carbon dioxide present in the air. This reaction leads to the formation of compounds such as copper carbonate and copper hydroxide.

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