When solid aluminum chloride (AlCl3) forms Al2Cl6, what type of bond is present between the molecules?

The correct answer is Coordinate. In the compound Al₂Cl₆, the bond between the two AlCl₃ molecules is a coordinate covalent bond (also called a dative bond). This occurs when one AlCl₃ molecule shares a pair of electrons from a chlorine atom with the electron‑deficient aluminum atom of the other AlCl₃ molecule. Each aluminum atom is bonded to four chlorine atoms through coordinate bonds, resulting in a bridged structure. Ionic and covalent bonds exist within the AlCl₃ units, but the bond between the molecules is coordinate. Therefore, the correct type of bond is coordinate.