Lattice energy is the energy released when gaseous ions combine to form one mole of a crystalline ionic compound. According to Coulomb's law, lattice energy is directly proportional to the product of ionic charges and inversely proportional to the interionic distance (sum of ionic radii). Since all four compounds share the same cation Na^+ and have the same ionic charges, the lattice energy depends mainly on the size of the anion. Fluoride (F^-) is the smallest halide ion with a radius of about 133 pm, while chloride, bromide, and iodide are progressively larger (181, 196, and 220 pm respectively). Smaller interionic distance in NaF means stronger electrostatic attraction and therefore higher lattice energy. NaI has the lowest lattice energy because iodide is the largest anion, maximising the interionic distance and weakening the electrostatic force. NaCl and NaBr have intermediate values. This pattern follows the NCERT-discussed Born-Haber cycle trend and is consistent with the higher melting point of NaF compared to other sodium halides. Verification: lattice energy of NaF (~923 kJ/mol) > NaCl (~788 kJ/mol) > NaBr (~741 kJ/mol) > NaI (~700 kJ/mol), confirming the trend.