Mg --> Mg
2+ + 2e
- E=2.38V
O
2 + 2H
2O + 4e
- --> 4OH
- E= 0.40V
or if you de-oxygenate the water first (protons supplied by the water equilibrium):
2H
+ + 2e
- --> H
2 E = 0V
what do you think would happen if you get pure magnesium in contact with water?
Burning sulfur can be achieved in pure oxygen - the content in air is too low.
See
here for a good example. If you want to try this BE SAFE, working with flammables and pure oxygen is very hazardous. And the fumes are dangerous (think of the origin of acid rain), the create strong acids on contact with water.