Step 1: Understand factors affecting melting point of ionic compounds.
Melting point mainly depends on lattice energy.
Higher lattice energy → stronger ionic bonding → higher melting point.
Lattice energy depends on:
• Charge on ions
• Size of ions (smaller size → stronger attraction)
Step 2: Compare the given compounds.
(A) LiBr → Li is very small and highly polarizing. It increases covalent character (Fajan's rule), lowering melting point.
(B) NaBr → Na is larger than Li and less polarizing. Hence, bonding is more ionic and lattice energy remains high.
(C) MgBr → Though Mg has higher charge, it strongly polarizes Br , increasing covalent character and reducing melting point.
(D) AlBr → Highly covalent in nature and exists as dimer (Al Br ), so it has low melting point.
Step 3: Conclusion.
Among the given options, NaBr is the most ionic and thus has the highest melting point.