Which of the following sublimes on heating?

Which of the following does not liberate $H_2$ gas upon reaction with an acid?

On the basis of reactions given below identify $X, Y, Z$.
$Boron \xleftarrow{Mg \, or \, Fe} X \xleftarrow{\Delta} B(OH)_3 + \text{Gas-}Z$
$B(OH)_3 \xleftarrow{H_2O} Y \xrightarrow{2NH_3/\Delta} \text{Inorganic benzene}$

The correct statements from the following are $:$
$(A)$ $Tl^{3+}$ is a powerful oxidising agent
$(B)$ $Al^{3+}$ does not get reduced easily
$(C)$ Both $Al^{3+}$ and $Tl^{3+}$ are very stable in solution
$(D)$ $Tl^{+}$ is more stable than $Tl^{3+}$
$(E)$ $Al^{3+}$ and $Tl^{+}$ are highly stable
Choose the correct answer from the options given below $:$

The stability of $+1$ oxidation state among $Al$,$Ga$,$In$ and $Tl$ increases in the sequence:

Boron halides behave as Lewis acids because of their