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

Aluminium $(III)$ chloride forms a dimer because ........

Which of the following reactions can be used to prepare diborane?
$I. BF_3 + LiAlH_4 \xrightarrow{\text{ether}}$
$II. BF_3 + NaH \xrightarrow{450 \ K}$
$III. Na_2B_4O_7 + H_2O \longrightarrow$
$IV. NaBH_4 + I_2 \longrightarrow$

Relative stability orders of $+1$ and $+3$ oxidation states of $Ga, In, Tl$ are respectively:

In a molecule of pyrophosphoric acid $(H_4P_2O_7)$,the number of $P-OH$,$P=O$ and $P-O-P$ bonds/moiety(ies) respectively are:

Identify the correct statements about Boron.
$I.$ It has a high melting point.
$II.$ It has a high density.
$III.$ It has high electrical conductivity.
$IV.$ The $^{10}B$ isotope of it has a high ability to absorb neutrons.