3 Na2S2O3 (aq) + H2SO4 (aq) → 3 Na2SO4 (aq) + 4 S (s) + H2O (l)
This is an oxidation-reduction (redox) reaction:
4 SII + 8 e- → 4 S0 (reduction)
2 SII - 8 e- → 2 SVI (oxidation)
Na2S2O3 is both an oxidizing and a reducing agent (disproportionation (dismutation)).
This is a precipitation reaction: S is the formed precipitate.