Explanation:
The melting point of a compound is dependent on several factors such as the strength of the intermolecular forces, size and charge of the ions, and lattice energy. In this case, the melting point of NaF is higher than the other three compounds due to the following reasons:

Ionic Character:
NaF has the highest ionic character among the given compounds. This is because the difference in electronegativity between Na and F is the highest among the given compounds. As a result, the bond between Na and F is highly polar covalent, and the F ion has a high negative charge. This leads to stronger electrostatic forces of attraction between the oppositely charged ions, resulting in a higher melting point.

Lattice Energy:
The lattice energy of NaF is the highest among the given compounds. This is because the F ion is the smallest among the given anions, and NaF has the highest charge density. The high charge density leads to a higher attraction between the ions, resulting in a higher lattice energy. The high lattice energy contributes to the high melting point of NaF.

Size and Charge of Ions:
The size and charge of the ions also play a role in the melting point of a compound. In this case, NaBr and NaI have larger anions, which means that the distance between the ions in the lattice is greater. This leads to weaker electrostatic forces of attraction and a lower melting point. Additionally, NaCl and NaBr have smaller charges on their anions, resulting in weaker electrostatic forces and lower lattice energies.

In conclusion, NaF has the highest melting point among the given compounds due to its high ionic character, high lattice energy, and small size of the F ion.