The number of three-centre two-electron $(3c-2e)$ bonds in a molecule of diborane $(B_2H_6)$ is

Identify the compounds $A$,$X$ and $Z$ in the following reactions :
$A + 2HCl + 5H_2O \to 2NaCl + X$
$X$ $\xrightarrow[370 \ K]{\Delta} HBO_2$ $\xrightarrow[> 370 \ K]{\Delta} Z$

What is the correct formula for Borazole?

What is added to borax to obtain boric acid?

In the following reactions:
$3B_2H_6 + 6NH_3 \text{ (excess)} \xrightarrow{\Delta} 2B_3N_3H_6 + 12H_2$
$6NaH + 2BF_3 \xrightarrow{450 \ K} B_2H_6 + 6NaF$
$B_2H_6 + 6H_2O \longrightarrow 2H_3BO_3 + 6H_2$
$X, Y$ and $Z$ are respectively:

In the structure of diborane $(B_2H_6)$,the number of $2$-centre-$2$-electron $(2c-2e)$ bonds is $X$ and the number of $3$-centre-$2$-electron $(3c-2e)$ bonds is $Y$. The value of $(X+Y)$ is: