Which of the following substances has the highest boiling point?

• A. NH_3
• B. CO_2
• C. CH_4
• D. H_2O

Answer: (D)

Verified step by step guidance

1. Identify the types of intermolecular forces present in each substance: NH_3, CO_2, CH_4, and H_2O. These forces influence boiling points significantly.
2. Recognize that NH_3 and H_2O can form hydrogen bonds because they contain N-H and O-H bonds, respectively, while CO_2 and CH_4 primarily exhibit London dispersion forces due to their nonpolar nature.
3. Understand that hydrogen bonding is a much stronger intermolecular force compared to dipole-dipole interactions or London dispersion forces, leading to higher boiling points.
4. Compare the strength of hydrogen bonding in NH_3 and H_2O. Water (H_2O) has stronger hydrogen bonding because oxygen is more electronegative than nitrogen and it can form two hydrogen bonds per molecule, whereas NH_3 forms fewer.
5. Conclude that H_2O has the highest boiling point among the given substances due to its strong hydrogen bonding, followed by NH_3, with CO_2 and CH_4 having much lower boiling points because of weaker intermolecular forces.