Trends in Volatility of Halogens Down Group 17

Steps:

• Atomic size increases from Cl to I, leading to stronger van der Waals forces between molecules.
• Stronger van der Waals forces raise boiling points, reducing volatility.
• Volatility is inversely related to boiling point; higher boiling point means lower volatility.
• Thus, volatility decreases as van der Waals forces increase.

Why C is correct:

• Volatility decreases down the group because larger atomic size induces stronger London dispersion forces (van der Waals), increasing intermolecular attractions and boiling points.

Why the others are wrong:

• A: Hydrides become stronger reducing agents down the group due to weaker H-X bonds, not weaker.
• B: Identical to C but uses possessive "van der Waals'" incorrectly; standard term is "van der Waals forces."
• D: Volatility decreases, not increases, with molecular size due to enhanced van der Waals forces.

Final answer: C