Intermolecular forces explain higher melting point of iodine

Steps:

• Both chlorine (Cl₂) and iodine (I₂) are nonpolar diatomic molecules, so intermolecular forces dominate melting points.
• For nonpolar molecules, London dispersion forces (instantaneous dipole-induced dipole) are the key intermolecular attractions.
• These forces increase with molecular size and number of electrons, making larger I₂ have stronger attractions than smaller Cl₂.
• Stronger forces require more energy to overcome, resulting in iodine's higher melting point.

Why D is correct:

• Instantaneous dipole-induced dipole forces (London dispersion) strengthen with atomic size due to greater electron cloud polarizability, as per the trend in van der Waals forces for halogens.

Why the others are wrong:

• A: Covalent bonds are intramolecular and similar in strength; they do not directly cause higher melting points in molecular solids.
• B: Neither molecule has permanent dipoles, as both are symmetrical and nonpolar.
• C: Higher melting point indicates lower volatility for iodine, not higher.

Final answer: D