Question

why most of the metal articles become dull when exposed in air?

Answer 1

This happens due to the process called Oxidization. The moist air present their reacts with the metal and as a result metal articles loss their shiny texture. This can be prevented by covering the surface of metal articles with any other compound such as paint.
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Answer 2

hello friend,
Most of the metal articles become dull when exposed in air because metal react with oxygen to form metallic oxide which is basic in nature and makes the appearence of the article dull.
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