Read the following question and answer:
 
A shiny metal 'X', when kept in the open, reacts slowly with sulphur compounds in the air to form a black coating 'Y'.
i. Identify 'X' and 'Y'.
ii. Write the balanced chemical equation.
iii. Name the process involved.
 
i. 'X' is and 'Y' is .
 
ii. The balanced chemical equation is.
 
iii. The process is called as.