Final answer:
Water (H₂O) is capable of forming hydrogen bonds with itself in the liquid state due to the presence of hydrogen atoms bonded to a highly electronegative oxygen atom, along with lone pairs on the oxygen that can act as acceptors.
Step-by-step explanation:
The compound capable of hydrogen bonding with itself in the liquid state among the choices provided is water (H₂O). This is because water molecules have a hydrogen atom bonded to an oxygen atom, which is highly electronegative. The oxygen atom also has two lone pairs of electrons that can act as hydrogen bond acceptors. Water, therefore, can form a strong hydrogen bond network in its liquid state, which gives it unique properties such as a high boiling point and high surface tension.
Ethanol (C₂H₅OH) is also capable of hydrogen bonding because it possesses an -OH group similar to water. Methane (CH₄) and carbon dioxide (CO₂) cannot form hydrogen bonds because they lack hydrogen atoms bonded to highly electronegative atoms like oxygen or nitrogen, which are necessary for creating hydrogen bonds.