why is potassium fluoride, Kg, more stable than the elements potassium and fluoride that comprise it?

Answer 1

potassium fluoride kf is more stable as a compound is formed to attain stability , bond formation takes place only if the new compound is more stable or if an excess of energy is given

potassium has 1 valence electron and it needs to loose it so that it attains noble gas config
fluorine has 7 valence electron and needs 1 to attain noble gas config so k looses one and f gains one to form kf

Answer 2

Potassium Fluoride is KF, not Kg....

Anyway, the compound is more stable because of the nature of the ions which make it up. In Potassium Fluoride, there are potassium ions and fluoride ions. Both ions have a full valence shell of electrons, which makes them very stable.

Potassium and Fluorine as elements have incomplete valence shells making them less stable.