Fe0 + 2 NaCl + 2 H2IO H20 + FeIICl2 + 2 NaOHI

This is an oxidation-reduction (redox) reaction:

2 HI + 2 e- 2 H0 (reduction)

Fe0 - 2 e- FeII (oxidation)

H2O is an oxidizing agent, Fe is a reducing agent.