Which of the following has a coordinate bond?

In the reaction $BCl_3 + PH_3 \rightarrow Cl_3B^{-}PH_3$,the Lewis base is:

Give the structure of gaseous $AlCl_3$.

In $BF_3$,the $B-F$ bond length is $1.3 \ \mathring{A}$. When $BF_3$ reacts with $Me_3N$,it forms an adduct $Me_3N \to BF_3$. In this adduct,the $B-F$ bond length will be ..........

Coordinate covalent compounds are formed by

In the reaction $NH_3 + BF_3 \rightleftharpoons NH_3 \to BF_3$,$BF_3$ is