Final answer:
A polar covalent bond will form between oxygen and fluorine because they have different but high electronegativities, resulting in a polar bond. The correct option is D. oxygen and fluorine.
Step-by-step explanation:
Between which pair of elements will a polar covalent bond form? When considering bond polarity, we refer to the concept of electronegativity, which is the tendency of an atom to attract electrons towards itself in a chemical bond. The greater the difference in electronegativity between two atoms, the more polar the bond is. Oxygen and fluorine both have high electronegativities but differ enough to form a polar covalent bond.
On the other hand, iodine and iodine (a pair of the same element) will form a nonpolar covalent bond, strontium and fluorine will likely form an ionic bond due to the significant difference in electronegativity and francium and fluorine would also form an ionic bond. Therefore, the bond between oxygen and fluorine is the correct answer as it is definitely polar covalent.