Question

Why h2so4 is act as a oxidant where h2s act as reductant?

Answer 1

Because h2so4 has oxygen which leads to oxidation whereas in h2s there is no oxygen molecule

Answer 2

In H2SO4 sulphur is in +6 oxidation state which is maximum for sulphur. So it can't lose more electron and can only gain electron and get reduced. When one get reduced other get oxidised, so it act as oxidant.

In H2S sulphur is in -2 oxidation state which is minimum so it can't gain more electron so it oxidises itself by losing electron and reduce others and act as reductant.