We’re being asked to arrange the given bonds in order of increasing ionic character.
The sharing of electrons by two non-metals forms a covalent bond.
The transfer of an electron from metal to non-metal forms an ionic bond.
The following table shows the type of bond according to the difference of electronegativity.
The higher the electronegativity difference, the more ionic a bond is.
How would you arrange the following bonds in order of increasing ionic character: C−F, O−F, H−F, and Na−F?