Silver article turns black when kept in the open for a few days due to formation of

When silver articles kept in the open place for few days, it will absorb sun light and reacts with ${\text{H}}_{\text{2}}\text{S}$and oxygen to form a black silver sulphide. The balanced chemical equation is

$4\text{Ag}+2{\text{H}}_{\text{2}}\text{S}+{\text{O}}_{\text{2}}\to \underset{\text{Black\hspace{0.17em}colour}}{2{\text{Ag}}_{\text{2}}\text{S}}+2{\text{H}}_{\text{2}}\text{O}$