Which one of the following substances should exhibit hydrogen bonding in the liquid state? PH3, He, H2S, CH4, CH3OH

The substance that should exhibit hydrogen bonding in the liquid state is CH3OH (methanol).

Here's why:

Hydrogen bonding is a special type of dipole-dipole attraction between molecules, where a hydrogen atom bonded to a highly electronegative atom exists in the vicinity of another electronegative atom with a lone pair of electrons. The highly electronegative atoms that participate in hydrogen bonding are typically nitrogen, oxygen, or fluorine.

Looking at the options:

1. PH3: Phosphorus is not highly electronegative, so it does not form hydrogen bonds.
2. He: Helium is a noble gas and does not form bonds easily, so it does not form hydrogen bonds.
3. H2S: Sulfur is not as electronegative as nitrogen, oxygen, or fluorine, so it does not form hydrogen bonds.
4. CH4: Carbon is not highly electronegative, so it does not form hydrogen bonds.
5. CH3OH: The OH part of the molecule can form hydrogen bonds. Oxygen is highly electronegative and hydrogen is attached to it. This hydrogen can form a hydrogen bond with the oxygen of another molecule.

So, CH3OH (methanol) is the substance that should exhibit hydrogen bonding in the liquid state.