Final answer:
Potassium iodide (KI) (option C) is expected to have the lowest melting point among the choices due to its large anion, leading to lower charge density and weaker Coulombic interactions.
Step-by-step explanation:
The question asks which ionic compound among KF, NaI, KI, and NaCl has the lowest melting point. When comparing ionic compounds, we look at ionic lattice energies and polarizing abilities of the ions. Ionic compounds with lower charge densities typically have lower lattice energies, which correlates with lower melting points. Compounds with ions having a larger size and lower charge are predicted to have lower melting points due to weaker Coulombic interactions.
Comparing the given compounds, potassium iodide (KI) would be expected to have the lowest melting point. This is because KI has the largest anion (iodide, I-) which leads to lower charge density compared to the smaller anions in KF and NaCl. The presence of the larger potassium (K) cation contributes to decreasing the lattice energy further due to the increased interionic distance. Additionally, CsI, which is similar in structure to KI but with even larger cations and anions, has a relatively low melting point as well which supports this conclusion.