Silver does not combine easily with oxygen but silver jewellery tarnishes after some times. How?

Explanation

Silver reacts with sulphur compounds like hydrogen sulphide present in air in trace amount to form silver sulphide which gets coated on silver as black layer. So, silver jewellery becomes dull after prologned use.
Equation: Silver + Hydrogen sulphide `to` Silver sulphide
`Ag + H_2 S to Ag_2 S` (Black)