Al2Cl6 Dimer Structure and Bonding Steps:

• Molecular mass M=267 confirms Al2Cl6 (2×27 + 6×35.5 = 267), not monomeric AlCl3 (133.5).
• In Al2Cl6, each Al connects to four Cl: four terminal Al–Cl bonds are covalent; two bridging Cl form two additional covalent bonds and two dative bonds (Cl → Al).
• Total: 6 covalent bonds (4 terminal + 2 bridge) and 2 dative bonds.
• Each of 6 Cl atoms contributes 3 lone pairs (7 valence e – 1 for bonding = 6 e or 3 pairs), totaling 18 lone pairs.

Why B is correct:

• Matches Al2Cl6 bonding model: 6 shared-electron covalent bonds, 2 coordinate dative bonds, and 18 lone pairs on Cl atoms per Lewis structure.

Why the others are wrong:

• A: Incorrectly states 0 lone pairs; Cl atoms have lone pairs to achieve octet.
• C: Duplicate of B; no distinction.
• D: Describes monomeric AlCl3 (3 covalent bonds, 9 lone pairs), but M=267 indicates dimer.

Final answer: B