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Conc.H2SO4 being strong Oxidising agent causes reaction:

Ag2S + Conc.H2SO4→Ag2O + SO2 +H2O

In which sulphide is oxidised to SO2 which will move out due to it being a gas . SO2 can act as both oxidizing as well as reducing agent since it has +4 oxidation state which is exactly between its highest oxidation state +6 and lowest oxidation state +2 ,Thus it can change its oxidation number either from +4 to-2( reduction ) and +4 to+6 . silver and sulfuric acid could react due to a reduction of sulfuric acid do SO 2 .