When $AlCl_3 \cdot 6H_2O$ is strongly heated,then it forms

Which of the following compounds of boron is the hardest?

Given below are two statements:
Statement $I$: Group $13$ trivalent halides get easily hydrolyzed by water due to their covalent nature.
Statement $II$: $AlCl_3$ upon hydrolysis in acidified aqueous solution forms octahedral $[Al(H_2O)_6]^{3+}$ ion.
In the light of the above statements,choose the correct answer from the options given below:

What are the correct statements about the elements of group $13$ given below?
$(I)$ The stability of $+1$ oxidation state follows the order $Tl > In > Ga$
$(II)$ Boron has the lowest melting point and boiling point as it is a non-metal
$(III)$ Boron shows a maximum covalency of $4$ in its compounds
$(IV)$ The order of atomic radius is $Ga > Al > In$
$(V)$ Aluminium is passive to concentrated nitric acid

Identify the correct statements:
$i$. Oxidation of $NaBH_4$ with $I_2$ gives $B_2H_6$
$ii$. $B_2H_6$ burns in oxygen and releases an enormous amount of energy
$iii$. $B_2H_6$ on hydrolysis gives a tribasic acid

Diborane reacts with ammonia to form $X$, which on heating gives $H_2$ and borazine. $X$ is