2 Mg0 + O20 + 2 H2O-II 2 MgII(O-IIH)2

This is an oxidation-reduction (redox) reaction:

2 Mg0 - 4 e- 2 MgII (oxidation)

2 O0 + 4 e- 2 O-II (reduction)

Mg is a reducing agent, O2 is an oxidizing agent.