Answer:
Most exothermic
Kl
KBr
KCl
KF
Most endothermic
Explanation:
There is the presence of the same cation in the given salts, so only anion has to be compared.
The charge density of the anion decreases from the fluoride to the iodide as size increases from fluoride to iodide. Fluoride has highest charge density because of the smallest radius in halogen family. Also, potassium fluoride would have highest lattice enthalpy because there will be greater force of attraction between them. The trend for the lattice enthalpy is:
KF>KCl>KBr>KI
Since more energy to split KF , so it will be most endothermic and so on.
So trend is:
KF is most endothermic and KI being most exothermic.
Most exothermic
Kl
KBr
KCl
KF
Most endothermic