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Why do some metals acquire a dull appear...

Why do some metals acquire a dull appearance on exposure to air for a long time ?

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### Step-by-Step Solution: 1. **Understanding the Question**: The question asks why some metals develop a dull appearance when exposed to air over a long period of time. 2. **Exposure to Air**: When metals are exposed to air, they interact with various components present in the atmosphere, such as oxygen, carbon dioxide, and sulfur dioxide. 3. **Formation of Compounds**: Some metals react with these atmospheric components to form different compounds. For example: - **Copper**: When copper is exposed to moisture and air, it can react to form copper hydroxide (Cu(OH)₂) and copper carbonate (CuCO₃). This results in the formation of a layer that gives copper a dull appearance. ...
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