Correct Answer - Although `O` and `Cl` have about the same electronegativity and small size (covalent radii) are much different : O=66` pm and `Cl=99` pm.As a result, electron density per unit volume on oxygen atom is much higher than that on chlorine atom.Therefore, oxygen forms hydrogen bonds while chlorine does not even though both have approx. the atoms. the same electronegativity.
