Which of the following compounds has the highest boiling point?

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

Answer: (C)

Verified step by step guidance

1. Step 1: Understand that boiling point depends on the strength of intermolecular forces present in the compound. Stronger intermolecular forces lead to higher boiling points.
2. Step 2: Identify the types of intermolecular forces in each compound: CO_2 and CH_4 are nonpolar molecules with London dispersion forces; NH_3 is polar and exhibits hydrogen bonding; H_2O is also polar and exhibits strong hydrogen bonding.
3. Step 3: Compare the strength of intermolecular forces: London dispersion forces < dipole-dipole interactions < hydrogen bonding. Since H_2O has strong hydrogen bonding, it will have a higher boiling point than NH_3, CO_2, and CH_4.
4. Step 4: Recognize that molecular weight also affects boiling point but is less significant than hydrogen bonding in this case. CO_2 has a higher molecular weight than CH_4 but weaker intermolecular forces, so it has a lower boiling point.
5. Step 5: Conclude that H_2O has the highest boiling point due to its strong hydrogen bonding, which requires more energy (heat) to break during the phase change from liquid to gas.