Final answer:
Among NaI, NaF, MgO, MgCl2, and KF, MgO is expected to have the highest melting point due to its highest lattice energy, which is a result of the strong ionic bonding between Mg2+ and O2- ions.
Step-by-step explanation:
To determine which solid has the highest melting point among NaI, NaF, MgO, MgCl2, and KF, we have to consider the lattice energies of the compounds which typically relate to the ionic charges and the sizes of the ions. The melting points of ionic compounds are influenced by lattice energies, and generally, the higher the lattice energy, the higher the melting point.
Since MgO has ions with higher charges (Mg2+ and O2-) and a smaller interionic distance, it would have a significantly higher lattice energy compared to the salts with mono-valent ions, making it the solid with the highest melting point among the given options.
The relationship between melting point, lattice energy, and solubility indicates that solids like MgO with high lattice energies are not only harder and have higher melting points but are also less soluble in water. Therefore, MgO would be expected to have the highest melting point due to its high lattice energy caused by strong ionic bonding between Mg2+ and O2-.
Comparatively, NaF, MgCl2, NaI, and KF have lower charges on their ions and greater distances between ions, which result in lower lattice energies and consequently, lower melting points than MgO.