Concept:Electronegativity determines the attraction of a bonded pair of electrons towards an atom in a covalent bond.Explanation:In a hydrogen chloride molecule, the shared pair of electrons is attracted by both atoms.Chlorine has a higher electronegativity than hydrogen.This stronger attraction pulls the bonding electron pair closer to the chlorine atom.This unequal sharing makes the bond polar.The atomic size or atomic mass of chlorine is not the reason for this pull.Answer:C. chlorine is more electronegative