Intermolecular forces explain decreasing volatility in Group 17

Steps:

• Volatility relates to boiling point; higher boiling point means lower volatility.
• Down Group 17, atomic size increases, enhancing London dispersion forces.
• Stronger forces raise boiling points, decreasing volatility.
• Option A correctly identifies instantaneous dipole-induced dipole forces (London forces) as the cause.

Why A is correct:

• London dispersion forces increase with molecular size and polarizability, per van der Waals theory, leading to stronger attractions and higher boiling points.

Why the others are wrong:

• B: Halogens are diatomic nonpolar molecules, so permanent dipole-dipole forces are negligible.
• C: Bond energy of X₂ increases down the group, not decreases, but this affects decomposition, not volatility.
• D: Ionization energy decreases, but volatility depends on intermolecular forces, not ionization.

Final answer: A