The answer is: the greatest difference in electronegativity have K and F.
Electronegativity (χ) is a property that describes the tendency of an atom to attract a shared pair of electrons.
Atoms with higher electronegativity attracts more electrons towards it, electrons are closer to that atom.
For example fluorine has electronegativity χ = 4 and potassium χ = 0.82, fluorine attracts electron and it has negative charge and sodium has positive charge.
Δχ(K-F) = 4 - 0.82.
Δχ(K-F) = 3.18; electronegativity difference between potassium and fluorine.
When the electronegativity difference is greater, the bond polarity is increasing.
