Answer:
XY would have a higher melting point than NaCl.
Explanation:
The electrostatic force (F) between ions in an ionic lattice can be estimated using Coulomb's Law.
where,
k is the Coulomb's constant
q₁ and q₂ are the charges of the ions
r is the distance between the ions
X⁺⁺ and Y⁻⁻ are doubly charged with respect to Na⁺ and Cl⁻ so the force between them is 4 times the force between Na⁺ and Cl⁻. Since the force is stronger, it would require more energy to break it to take it to the liquid state, so a higher melting point is expected.