Volatility depends on strength of London dispersion forces

Steps:

• Chlorine (Cl₂) is more volatile than bromine (Br₂) due to lower boiling point.
• Instantaneous dipole-induced dipole forces (London dispersion) increase with molecular size and electron count.
• Br₂ has larger atoms and more electrons than Cl₂, leading to stronger forces in Br₂.
• Weaker forces in Cl₂ result in easier evaporation, confirming Cl₂'s higher volatility.

Why C is correct:

• C correctly states Cl₂ is more volatile because dispersion forces are stronger in Br₂ (larger molecule) than in Cl₂, per the trend in halogens.

Why the others are wrong:

• A: Incorrectly claims Br₂ is more volatile despite stronger forces in Br₂, contradicting the volatility explanation.
• B: Wrongly identifies Br₂ as more volatile and reverses force strength (stronger in Cl₂).
• D: Misstates force strength by claiming they are greater in Cl₂ than Br₂, inverting the actual trend.

Final answer: C