Question

a student has been collecting silver with black coating and cooper coins with green coating.which chemical phenomena is responsible forctjese coatings?what is the chemical name of black and green coating.

Answer 1

Silver reacts with oxygen, hydrogen sulphide and moisture in the air and a black coated layer is formed over it and then it becomes silver sulphide.

Copper reacts with oxygen, carbonates and moisture in the air and a green coated layer is formed over it and then it becomes copper carbonate.

hope this helps you...
plz mark it as a brainliest answer...

Answer 2

when silver reacts with Hydrogen Sulphide present in the air it forms a layer of Silver Sulphide which is black in colour.
When Copper Metal is exposed to moist air it forms a layer of basic Copper Carbonate which is green in colour. 
the phenomenon responsible is corrosion.