Draw the structures of `BCl_(3).NH_(3) and AlCl_(3)` (dimer).

Explanation

In the `BCl_(3)`, due to small size of `B^(3+),BCl_(3)` is covalent. Still, the octet of B remains incomplete. In `NH_(3)`, N has a lone pair of electron. Hence, N shares lone pair of electron with B to complete the octet. Hence, `BCl_(3)` acts as Lewis acid and `NH_(3)` as Lewis bases
`H_(3)N: BCl_(3) rarr H_(3)N rarr BCl__(3) or BCl_(3).NH_(3)`
`AlCl_(3)` forms dimer by completing octet of Al involving p-orbitals to accept electron pair from chlorine.