as we move down the groups, the ionic radii increases .when the distance between the ions in a crystal increases, lattice energy decreses. among the given ionic crystals LiF would have highest lattice energy. LiF > LiI > KF > KI > NaF Solution as we move down the groups, the ionic radii increases .when the distance between the ions in a crystal increases, lattice energy decreses. among the given ionic crystals LiF would have highest lattice energy. LiF > LiI > KF > KI > NaF.