Question

silver articles become black after sometime when exposed is air

Answer 1

this is because the silver metal reacts with the sulphur present in the atmosphere and forms silver sulphide (black color)

Answer 2

The silver article becomes black after sometimes when exposed to air because silver reacts with sulphur which is present in the atmosphere and then forms silver sulphide. Thus the layer of this silver sulphide is formed on the surface of the silver article so they appear as dull or black