Answer:
4Al(s) + 3O2(g) ---------->2Al2O3(s)
2Mg(s) + O2(g) ------------>2MgO(s)
3Fe(s) + 2O2(g) -------------> Fe3O4(s)
Step-by-step explanation:
Aluminum reacts with moist air forming a coat of aluminum oxide. This oxide formed prevents further reaction of the metal with atmospheric oxygen or water under normal circumstances.
Magnesium undergoes oxidation in moist air forming a film of magnesium oxide because it is a very electripositive metal and has strong affinity for oxygen.
Iron on exposure to air, gradually rusts as a result of the hydrated iron (111) oxide formed. This reaction continues until all the iron has been converted to the oxide as the iron (III) does not prevent further reaction.
But on heating, finely divided iron combines with oxygen to firm iron (II) diiron(III) oxide.