Question

Give reason that the shining surface of some metals becomes dull when exposed to air for a long time

Answer 1

When some metals get exposed to air there is an oxidation process occurring on the outer layer of the metal. Due to the oxidation; a new layer covers the existing metal; hiding its original view; giving it a dull appearance. Almost all metals combine with oxygen to form metal oxides.

Metal + Oxygen → Metal oxide

Answer 2

the surface of some metals becomes dull when exposed to air for long time because the metal reacts with air to form metal oxide layer on the metal surface so thats why it becomes dull



hope this helps