Final answer:
The least polar molecule among HF, HI, Br2, OH, and HCl is HI, as it has the smallest difference in electronegativity between the bonded atoms due to iodine being less electronegative.
Step-by-step explanation:
The question asks which of the given molecules is the least polar. Polar molecules are characterized by the presence of polar bonds, where there is a difference in electronegativity between the bonded atoms. Fluorine (F) is the most electronegative element, followed by oxygen (O), chlorine (Cl), bromine (Br), and iodine (I), in that order. The molecule with the least difference in electronegativity between the bonded atoms will thus be the least polar.
Hence, hydrogen iodide (HI) is the least polar molecule among the options provided. The reason is that iodine is less electronegative than the other halogens listed, and therefore the polarity of the H-I bond is lower than that of the H-F, H-Br, and H-Cl bonds. Additionally, OH (hydroxyl group) is typically quite polar due to the high electronegativity of oxygen.