Which of the following molecules can form a hydrogen bond with another identical molecule?

• A. C2H6
• B. CO2
• C. NH3
• D. CH4

Answer: (C)

Verified step by step guidance

1. Understand the criteria for hydrogen bonding: Hydrogen bonding occurs when a hydrogen atom is covalently bonded to a highly electronegative atom (usually nitrogen, oxygen, or fluorine) and is attracted to a lone pair of electrons on the same type of electronegative atom in another molecule.
2. Examine each molecule to identify if it contains hydrogen atoms bonded to N, O, or F: - C2H6 (ethane) has only C-H bonds, which are not sufficiently polar for hydrogen bonding. - CO2 (carbon dioxide) has no hydrogen atoms at all. - NH3 (ammonia) has hydrogen atoms bonded to nitrogen, which is highly electronegative and has lone pairs. - CH4 (methane) has only C-H bonds, similar to ethane, and cannot form hydrogen bonds.
3. Recognize that NH3 can form hydrogen bonds because the nitrogen atom has a lone pair and is bonded to hydrogen atoms, allowing intermolecular hydrogen bonding between NH3 molecules.
4. Conclude that among the given molecules, only NH3 meets the requirements to form hydrogen bonds with identical molecules.
5. Summarize that the presence of N-H, O-H, or F-H bonds and lone pairs on N, O, or F atoms in the molecule is essential for hydrogen bonding, which is why NH3 is the correct answer.