Boron compounds act as Lewis acids due to .....

Which of the following compounds of boron does not exist in the free form?

In moist air,$AlCl_3$ fumes because:

Is boric acid a protic acid? Explain.

The geometry around boron in the product '$B$' formed from the following reaction is
$BF_{3} + NaH \xrightarrow{450 \ K} A + NaF$
$A + NMe_{3} \rightarrow B$

The acidic strength of boron trihalides follows the order: