20. Select two substances that contain hydrogen bonds. 1) C_(3)H_(7)OH 2) HF 3) CO 4) C_(2)H_(4) 5) N_(2) Answer (score: 1):

The correct answer is 1) and 2) HF.Hydrogen bonding is a type of intermolecular force that occurs between a hydrogen atom bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) and another electronegative atom. In the given options, (propanol) and HF (hydrofluoric acid) both contain hydrogen atoms bonded to oxygen and fluorine, respectively, which are highly electronegative atoms. Therefore, they can form hydrogen bonds.