Chlorine is more volatile due to weaker London dispersion forces

Steps:

• Chlorine (Cl₂) has a lower boiling point than bromine (Br₂), making it more volatile.
• Both are nonpolar diatomic molecules, so intermolecular forces are instantaneous dipole-induced dipole (London dispersion) forces.
• Dispersion forces increase with molecular size and polarizability; Br₂ is larger than Cl₂, so forces are stronger in Br₂.
• Stronger forces in Br₂ raise its boiling point, confirming Cl₂'s higher volatility.

Why C is correct:

• London dispersion forces are greater in larger Br₂ than in smaller Cl₂, per the trend that polarizability increases down Group 17, leading to weaker forces and higher volatility in Cl₂.

Why the others are wrong:

• A: Incorrectly identifies Br as more volatile and wrongly states forces are greater in Br (should weaken volatility).
• B: Wrongly identifies Br as more volatile and reverses force comparison (forces are not greater in Cl).
• D: Correctly identifies Cl as more volatile but wrongly states forces are greater in Cl (opposite of size trend).

Final answer: C