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Question
Explain why, the surface of some metals acquires a dull appearance when exposed to air for a long time.
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Solution 1
Some metals, when exposed to air for a long time, react with oxygen in the atmosphere to form a dull layer of metal oxide on their surfaces. This makes the metals look dull.
Solution 2
Most of the metals are reactive towards air. They react with oxygen present in the air to form metal oxides. The metal oxide formation appears on the surface of the metals as a thin layer. This thin layer formation of metal oxide on the metallic surface causes the dull appearance of the metals. Thus, the surface of some metals acquires a dull appearance when exposed to air for a long time.
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