Question

the shining surface of metal becomes dull when exposed to air for long time . give reason,give little big answer​

Answer 1

£.shining surface of the metal becomes dull because of corrosion

corrosion.

£. when some metals like silver or copper exposed to air it becomes brown in colour which becomes corroded when kept in moisture

£.cu becomes green in colour

£.but aluminium do not corroded when kept in master because aluminium react with oxygen to form a thick layer on the top so it does not become corroded when kept in a moisture