Question

Why do metals lose their shine and appear dull after some time?

Answer 1

Explanation:

some metal often lose their shine and appear dull because of action of air and moisture on them .Eg iron becomes reddish brown because of rust. also some metals as a result of oxidation with atmospheric oxygen forms oxides and by which their appearance becomes dull .

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Answer 2

Answer:

The metals lose their shine on brightness on keeping in air for a long time due to formation of a thin layer of oxide, carbonate or sulphide on their surface by the slow action of various gases present in air.