The molecule with the strongest intramolecular bond is HF. Hydrogen fluoride is the answer due to the strong and highly electronegative nature of Fluorine.
Fluorine is the most electronegative element in nature.
When it combines with other substances, due to its electronegative property, it draws most of the electrons closest to itself in the bond.
This tendency and ability makes the shared electrons closer the fluorine in the bond.
The strong polarization that ensues confers a very strong covalent bond pair on the bond formed.
