6 KI (aq) + 4 H2SO4 (aq) → S (s) + 3 I2 (s) + 3 K2SO4 (aq) + 4 H2O (l)
This is an oxidation-reduction (redox) reaction:
SVI + 6 e- → S0 (reduction)
6 I-I - 6 e- → 6 I0 (oxidation)
H2SO4 is an oxidizing agent, KI is a reducing agent.
This is a precipitation reaction: S andI2 is the formed precipitate.