Aluminium chloride exists as dimer, $$Al_2Cl_6$$ in solid state as well as in solution of non-polar solvents such as benzene. When dissolved in water, it gives

When anhydrous aluminium chloride ($$Al_2Cl_6$$) is dissolved in water, it undergoes a highly exothermic hydration reaction rather than simple dissociation into bare ions.

Because of this high charge density, it exerts a strong electrostatic attraction on the lone pairs of polar water molecules. It undergoes extensive hydration to form a stable octahedral coordination complex.

Six water molecules coordinate with the aluminium ion to form the hexaaquaaluminium(III) complex cation, $$[Al(H_2O)_6]^{3+}$$. Meanwhile, the chloride ions dissociate completely into the solution as hydrated $$Cl^-$$ ions.

$$Al_2Cl_6(s) + 12\text{H}_2\text{O}(l) \rightarrow 2[Al(\text{H}_2\text{O})_6]^{3+}(aq) + 6\text{Cl}^-(aq)$$

Hence, Option D is correct