Final answer:
NaI has the lowest melting point among the given compounds as it has the largest halide ion, resulting in the lowest lattice energy and weakest electrostatic attractions.
Step-by-step explanation:
The student is asking which ionic compound among NaBr, NaCl, NaH, NaF, and NaI has the lowest melting point based on relative lattice energies. The lattice energy of an ionic compound is directly related to its melting point: the higher the lattice energy, the higher the melting point. Lattice energy is influenced by the size of the ions and the charge they carry; smaller ions and higher charges result in greater lattice energies.
When comparing ionic compounds that consist of a single positive ion (like Na+) paired with different negative ions, we expect the compound with the largest anion to have the lowest lattice energy. This is because larger anions result in greater internuclear distances between the ions, leading to weaker electrostatic attractions. Among the given compounds, NaI contains the largest halide ion (I−), which means it would have the weakest electrostatic attractions and thus the lowest lattice energy. As a result, NaI would have the lowest melting point among the options provided.