Expert Answers
gsenviro eNotes educator| Certified Educator

Magnesium oxide (MgO) is a base and not an acid. Magnesium is a metal and like most of the metals, it form basic oxides. When magnesium oxide reacts with water the following reaction takes place:

`MgO + H_2O -> Mg(OH)_2`

magnesium hydroxide is formed in this reaction. Since magnesium oxide accepts protons (H^+ ions), it is a base (as per Bronsted-Lowry definition of acids and bases). Acids, on the other hand, are donors of protons. 

Magnesium oxide is not a very strong base, especially when compared with group I oxide, such as sodium oxide (Na2O). 

Metal oxides are generally basic in nature, especially the first oxides where the highest oxidation state of the metal is involved. Aluminum oxide is a transitory compounds (shows properties of both acids and bases).



Hope this helps.