Final answer:
The type of crystal structure in magnesium oxide is ionic, and it has a high melting point due to the strong attractions between the ions in the crystal lattice.
Step-by-step explanation:
The type of crystal structure in magnesium oxide is ionic. Ionic crystals consist of alternating positively-charged cations and negatively-charged anions, and they have high melting points. Magnesium oxide has a high melting point because of the strong attractions between the ions in the crystal lattice. These attractions, known as electrostatic attractions, are much stronger than the partial charges in polar molecular compounds, resulting in the high melting point of magnesium oxide.