$AlCl _{3}+$ aqueous acid $\rightarrow\left[ Al \left( H _{2} O \right)_{6}\right]^{3+}$
$Al ^{3+}$ ions give a complex ion in which $Al ^{3+}$ ion form six coordinate covalent bonds with six $H _{2} O$ molecules. Hence, it shows $s p^{3} d^{2}$ hybridisation.
(Due to availability of vacant $3 d$ -orbitals.)
$A l=3 s^{2} 3 p^{1}$
$A l^{3 T}=3 s^{0}$
Four electron pairs denoted by $6H_{2}O$ molecules
