The correct option is E MgO
Option E is the correct answer. MgO is an ionic compound. It is formed by the transfer of electrons from Magnesium to Oxygen and thus it forms a cation and an anion. In general, ionic compounds have more melting point than covalent compounds. The rest of the compounds in the question are covalent where they form compounds by mutual sharing of electrons between the atoms. And hence all the other compounds have low melting point. MgO being the only ionic compound has higher melting point.