List the following bonds in order of increasing ionic character: potassium to iodine, carbon to oxygen, lithium to fluorine, boron to fluorine. (Enter the two elements of the bond into the appropriate box: KI, CO, LiF, BF)

CO < BF < KI < LiF

Explanation:

The magnitude of ionic character in a bond is dependent on the magnitude of electronegativity difference between the atoms in the bond.

Remember that no bond is 100% ionic or covalent according to Linus Pauling. However, the percentage ionic character depends on electronegativity difference between the bonding atoms and polarizability (Fajan's rules).

Between LiF and KI, Fajan's rules become very important. The Li^+ is small and highly polarizing.  The stronger the polarising power of the cation and the higher the polarisability of the anion the more covalent character is expected in a bond