why colour of a] iron become raddish 

 

                     b] silver become blackish

 

                      c]copper become green 

when exposed in atmosphere for longer period of time

 

write answer in form of chemical equation

a) Iron when comes in contact with moist air reacts to give rust which is a brown powder mainly hydrated iron(III)oxide(Fe₂O₃ .xH₂O).

4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃ .xH₂O

b) Silver gets tarnished when exposed to the atmosphere which contains pollutant H2S and forms a black coating of Ag₂S.

2Ag_(s) + H₂S_(g) → Ag₂S_(s) + H_2(g)

c) Copper forms a green deposit on its surface when exposed to moist air. This is usually basic copper(II)sulphate[3Cu(OH)₂.CuSO₄].