Answers

2014-09-22T22:41:49+05:30
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 
2 3 2
Onely silver ..wat abt copper dude!!!
sry..my mistake,,
2014-09-22T22:59:44+05:30
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 ..
2 5 2
Just with ...sulphur !!
oops my mistake...