Aluminium chloride in acidified aqueous solution forms an ion...

Aluminium Chloride in acidified aqueous solution forms octahedral ${\left[Al ( {H}_{2}O{)}_{6}\right]}^{3 +}$ ion.

${AlCl}_{3}\overset{}{\overset{\text{Acidified aqueous solution}}{\to}{\left[Al{\left({H}_{2}O\right)}_{6}\right]}^{3 +}}$

In this complex the $3d$ orbital of Al are involved and the hybridisation state of Al is ${sp}^{3}{d}^{2}$.

Hence, the answer is option A.