3 S (s) + 6 NaOH (aq) → 2 Na2S (aq) + Na2SO3 (aq) + 3 H2O (l)
This is an oxidation-reduction (redox) reaction:
2 S0 + 4 e- → 2 S-II (reduction)
S0 - 4 e- → SIV (oxidation)
S is both an oxidizing and a reducing agent (disproportionation (dismutation)).