Halogen group trends in physical properties

Steps:

• Recall halogens are Group 17 non-metals: F, Cl, Br, I, At.
• Identify trends: atomic size increases down the group due to added electron shells.
• Link size to properties: larger atoms mean stronger intermolecular forces, raising melting/boiling points.
• Evaluate options against trends: select the matching property.

Why B is correct:

• Melting points increase down the group because atomic size grows, enhancing van der Waals forces between molecules, requiring more energy to melt.

Why the others are wrong:

• A: Atomic size increases down the group due to additional electron shells, not decreases.
• C: Halogens form covalent molecular structures, so they do not conduct electricity when molten like ionic compounds.
• D: Silver salts of halogens (AgCl, AgBr, AgI) are insoluble in water; only AgF is soluble.

Final answer: B