Volatility and Intermolecular Forces in Halogens

Steps:

• Volatility inversely relates to strength of intermolecular forces; stronger forces mean higher boiling point and lower volatility.
• Both chlorine (Cl₂) and iodine (I₂) are nonpolar diatomic molecules, so intermolecular forces are temporary dipole-induced dipole (London dispersion) forces.
• Iodine has more electrons (106 vs. 34 in chlorine) and larger atomic size, leading to stronger dispersion forces.
• Thus, iodine's stronger forces make it less volatile than chlorine.

Why B is correct:

• London dispersion forces increase with the number of electrons, as more electrons create larger temporary dipoles that induce stronger attractions in neighboring molecules.

Why the others are wrong:

• A: Electronegativity difference doesn't cause repulsion between nonpolar molecules; it affects bond polarity, not intermolecular forces here.
• C: Bond energy refers to intramolecular bonds (Cl-Cl is actually stronger than I-I), but volatility depends on intermolecular forces, not bond breaking.
• D: Neither molecule has a permanent dipole, as they are homonuclear and nonpolar, so no permanent dipole forces exist.

Final answer: B