Which of the following substances has the highest boiling point?

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

Answer: (C)

Verified step by step guidance

1. Step 1: Understand that boiling point is influenced by the strength of intermolecular forces present in a substance. Stronger intermolecular forces result in higher boiling points because more energy is required to separate the molecules from the liquid phase to the gas phase.
2. Step 2: Identify the types of intermolecular forces present in each substance: NH_3, CH_4, H_2O, and CO_2. Consider hydrogen bonding, dipole-dipole interactions, and London dispersion forces.
3. Step 3: Recognize that H_2O and NH_3 can form hydrogen bonds because they have hydrogen atoms bonded to highly electronegative atoms (oxygen and nitrogen, respectively). CH_4 and CO_2 do not form hydrogen bonds; CH_4 is nonpolar with only London dispersion forces, and CO_2 is linear and nonpolar with only London dispersion forces.
4. Step 4: Compare the strength of hydrogen bonding in H_2O and NH_3. Water molecules form stronger and more extensive hydrogen bonds due to the two hydrogen atoms bonded to oxygen and the bent molecular shape, which allows for a more extensive hydrogen bonding network.
5. Step 5: Conclude that because H_2O has the strongest intermolecular forces (hydrogen bonding) among the given substances, it has the highest boiling point.