This is an oxidation-reduction (redox) reaction:
2 HI + 2 e- → 2 H0 (reduction)
K0 - 1 e- → KI (oxidation)
O-II - 1 e- → O-I (oxidation)
H2O is an oxidizing agent, K is a reducing agent, H2O is a reducing agent.
Reactants:
Products: