The polarity of the H-Cl bond in an HCl molecule is determined by the difference in electronegativity between the hydrogen H and chlorine Cl atoms. Electronegativity is the ability of an atom to attract electrons towards itself in a chemical bond.In the HCl molecule, hydrogen has an electronegativity value of 2.1, while chlorine has an electronegativity value of 3.16. The difference in electronegativity values is 3.16 - 2.1 = 1.06. Since the electronegativity difference is greater than 0.5, the H-Cl bond is considered polar.In a polar bond, the more electronegative atom in this case, chlorine attracts the shared electrons more strongly, resulting in a partial negative charge - on the chlorine atom and a partial positive charge + on the hydrogen atom. This creates a dipole moment in the HCl molecule, making it a polar molecule.