Question

why is sodium chloride has high melting and boiling point than magnesium chloride

Answer 1

hi friend,
The other chlorides are simple covalent molecules. Melting and boiling points: 

Sodium and magnesium chlorides are solids with high melting and boiling points because of the large amount of heat which is needed to break the strong ionic attractions.

Answer 2

Sodium has a valency of 1 hence it only needs to hold on to one atom of Chlorine to complete its octet hence the attraction is stronger as compared to MgCl2 which has to hold on to 2 atoms of Chlorine