If a solid line represents a covalent bond and a dotted line represents intermolecular attraction, which of these choices shows a hydrogen bond? --c- --o- --f- h-h

Generally, a hydrogen bond can be characterized as a proton shared by two lone electron pairs. It occurs when a hydrogen (H) atom, covalently bound to a highly electronegative atom such as nitrogen (N), oxygen (O), or fluorine (F), experiences the electrostatic field of another highly electronegative atom nearby.

   Among the choices in the bond (-N...H-O) one side of the Hydrogen is bonded to a highly electronegative atom with a lone pair (-N) and the other side is directly bonded with a highly electronegative atom (O-).

    So -N...H-O- shows a hydrogen bond.