Which of the following molecules can form hydrogen bonds?

• A. CO_2
• B. CH_4
• C. C_2H_6
• D. NH_3

Answer: (D)

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 such as nitrogen (N), oxygen (O), or fluorine (F), and this hydrogen interacts with a lone pair on another electronegative atom.
2. Examine each molecule to identify if it contains N, O, or F atoms bonded to hydrogen: CO_2 has carbon double bonded to oxygen but no hydrogen atoms; CH_4 and C_2H_6 have hydrogen atoms bonded to carbon, which is not electronegative enough to form hydrogen bonds.
3. Recognize that NH_3 (ammonia) contains nitrogen bonded to hydrogen atoms, and nitrogen is highly electronegative with lone pairs available, making it capable of hydrogen bonding.
4. Conclude that only molecules with N-H, O-H, or F-H bonds can form hydrogen bonds, so among the given options, NH_3 is the correct choice.
5. Summarize that the presence of N-H, O-H, or F-H bonds and lone pairs on N, O, or F atoms is essential for hydrogen bonding, which is why CO_2, CH_4, and C_2H_6 cannot form hydrogen bonds.