Question

silver articles become black when exposed to air why

Answer 1

When silver is exposed to air it becomes black due to the formation of a layer of oxide coating.....though silver is not a very reactive metal....bt with the passage of time it slowly reacts with the oxygen in the air and forms black coloured silver oxide......

*Silver is  not the only metal to do so...even gold articles become black 

Answer 2

Silver articles become black because they are gets coated with atmospheric Sulphur gas .
They are also called Self Protecting metal as the coating helps them to acquire waterproof and Moist proof coating around it ..