Answer:
Silver undergoes aerial oxidation and corrodes forming a black coating.
Silver Tarnishing
Silver reacts with sulphur and sulphur compounds in the air to give silver sulphide (Ag2S) which is black. Exposed silver forms Ag2S as it reacts with the H2S(g) in the atmosphere which is present due to certain industrial process.
2Ag(s) + H2S(g) → Ag2S(s) + H+2+(g)
