Final answer:
The solid with the lowest melting point among KI, KBr, KCl, and KF is KI, because the increasing size of the halide ions leads to weaker ionic bonds and lower melting points, with iodide being the largest of the given halide ions.
Step-by-step explanation:
The question is asking which of the following solids has the lowest melting point: A) KI, B) KBr, C) KCl, or D) KF. This question pertains to the concept of ionic solid melting points in chemistry. Ionic compounds typically have high melting points due to the strong electrostatic forces between the oppositely charged ions in the crystal lattice.
The melting point of an ionic solid can be affected by the size of the ions and the charge density. In this case, all options are alkali halides, which means they have similar structures and charge, but vary in ionic size. The trend in melting points for ionic compounds is that they decrease as the size of the anions increase. This is because larger anions form weaker ionic bonds due to less overlap with the cation's charge cloud.
Among the halides of potassium (K+), the size of the halide anions increases from fluoride (F-) to iodide (I-). Therefore, we would expect KF to have the highest melting point and KI to have the lowest melting point. This is corroborated by looking at actual melting points: KF melts at about 858 °C, KCl at about 771 °C, KBr at about 734 °C, and KI at about 681 °C.