Stronger London Dispersion Forces Due to Instantaneous Dipoles

Steps:

• Both IBr and ICl are diatomic interhalogen molecules with similar permanent dipole moments.
• Boiling points depend on intermolecular forces: dipole-dipole and London dispersion forces.
• London dispersion forces arise from instantaneous dipoles and increase with molecular size and polarizability.
• IBr has larger atoms (I and Br) than ICl (I and Cl), leading to greater polarizability and stronger instantaneous dipoles in IBr.

Why B is correct:

• Instantaneous dipoles cause London dispersion forces, which scale with molecular polarizability (α ∝ size); IBr's larger size yields stronger forces, raising its boiling point per the trend in nonpolar molecules like halogens.

Why the others are wrong:

• A: Incomplete phrase; lacks specificity on what is stronger.
• C: Both molecules have induced (dispersion) dipoles, but this doesn't explain the difference in strength.
• D: Both have permanent dipoles from electronegativity differences, so this doesn't account for IBr's higher boiling point.

Final answer: B