6 I2 (s) + 6 Ba(OH)2 (aq) → Ba(IO3)2 (s) + 5 BaI2 (aq) + 6 H2O (l)
This is an oxidation-reduction (redox) reaction:
10 I0 + 10 e- → 10 I-I (reduction)
2 I0 - 10 e- → 2 IV (oxidation)
I2 is both an oxidizing and a reducing agent (disproportionation (dismutation)).