When an Ionic Compound Melts, the Structure of the Crystal $\lt$

When an ionic compound melts, the structure of the crystal lattice breaks down, and the ions must be able to slip past each other.Using electrostatic potential energy as a guide, which listing of ionic compounds is in order of increasing melting point?

A) AlF₃ $\lt$ MgF₂ $\lt$ NaF
B) MgF₂ $\lt$ NaF $\lt$ AlF₃
C) NaF $\lt$ MgF₂ $\lt$ AlF₃
D) AlF₃ $\lt$ NaF $\lt$ MgF₂
E) NaF $\lt$ AlF₃ $\lt$ MgF₂