Orthoboric acid in aqueous medium is

What is the correct formula of Borazole?

Consider the following reactions.
$Na_{2}B_{4}O_{7} \xrightarrow{\Delta} 2 X + Y$
$CuSO_{4} + Y \xrightarrow{\text{Non-Luminous flame}} Z + SO_{3}$
$2Z + 2X + \text{Carbon} \xrightarrow{\text{Luminous flame}} 2Q + Na_{2}B_{4}O_{7} + CO$
The oxidation states of $Cu$ in $Z$ and $Q$,respectively are:

Identify the correct statements about the anomalous behaviour of Boron:
$I$. Boron trihalides can form dimeric structures.
$II$. Boron shows $+1$ as a stable oxidation state.
$III$. Maximum covalency of Boron is four.
$IV$. Boron does not form $BF_{6}^{3-}$ ion.

$Na_2B_4O_7 \stackrel{\text{heat}}{\longrightarrow} X + NaBO_2$
In the above reaction,the product $X$ is:

The most acidic of the following compounds is