Which of the following compounds has the lowest boiling point?

• A. H2O
• B. CH4
• C. NH3
• D. HF

Answer: (B)

Verified step by step guidance

1. Step 1: Understand that boiling point is influenced by the strength of intermolecular forces present in the compound. Stronger intermolecular forces generally lead to higher boiling points.
2. Step 2: Identify the types of intermolecular forces in each compound: H2O, NH3, and HF all exhibit hydrogen bonding, which is a strong type of dipole-dipole interaction, while CH4 primarily exhibits London dispersion forces, which are weaker.
3. Step 3: Recognize that hydrogen bonding occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine, leading to higher boiling points for H2O, NH3, and HF compared to CH4.
4. Step 4: Compare the molecular weights and structures: CH4 is a small, nonpolar molecule with only weak London dispersion forces, so it will have a lower boiling point than the others.
5. Step 5: Conclude that among the given compounds, CH4 has the lowest boiling point because it lacks hydrogen bonding and has only weak intermolecular forces.