Boron cannot form which one of the following anions?

Which of the following properties describes the diagonal relationship between boron and silicon?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$2Na[Al(OH)_4] + CO_2 \longrightarrow 2Al(OH)_3 \downarrow + Na_2CO_3$

The reason for boric acid being polymeric is .....

The alum used for purifying water is

Three pairs of compounds are given below. Identify the compound in each pair which has the group $13$ element in a more stable oxidation state. Give reasons for your choice and state the nature of bonding. $(A)$ $TlCl_3, TlCl$ $(B)$ $AlCl_3, AlCl$ $(C)$ $InCl_3, InCl$