Question

Why do silver articles turn black when kept on open?

Name the black substance formed and give its chemical formula?

Answer 1

they react with sulphur present in air to form silver sulphate which is black in color

Answer 2

As the silver articles react slowly with the hydrogen sulphide to form silver sulphide that is the black coloured compound.
AgS is the black coloured silver sulphide.
Ag + H2S ----> AgS + H2.