When BCl3 is treated with water, it hydrolysis and forms [B(OH)4]- on whereas AlCl3 in acidified aqueous solution forms [Al(H2O)6]3+ ion. Explain what is the hybridisation or boron and aluminium in these species ? 

In trivalent state, most of the compounds being covalent are hydrolysed in water, e.g., BC on hydrolysis in water form [B(OH)4]- species, the hybridisation state of B is sp3.
AlCl3 in acidified aqueous solution form octahedral [Al(H2O)6]3+ ion. In this complex, the 3d orbitals of Al are involved and the hybridisation state of Al is sp3d2.