Corrosion is the process in which metals are eaten up gradually by the action of air, moisture and chemicals on their surfaces.
Corrosion of copper:The Shine of copper objects slowly fades because of the layer of copper oxide formed on the surface on exposure to atmosphere.
Corrosion of few metals:
Sometimes we see green Coating on the surface of a copper object.
This is due the formation of basic copper Carbonate (CuCo3 Cu(oH)2) which is a mixture of Copper Carbonate and copper hydroxide.
The metal copper is low in the reactivity series and is less reactive. So the process is slow.
Silver gets tarnished when exposed to air. It gradually turns black due to formation of Silver Sulphide (Ag2S). The process is slow because Silver is less reactive.
Corrosion of silver:
The brown-flaky layer that we see on iron objects in due course of time is because of corrosion of iron. This is known as rusting of iron