Identify the correct statements from the following:
$a$) Borax gives blue coloured $Co(BO_2)_2$ when heated with $Co^{2+}$ salt.
$b$) The correct formula of Borax is $Na_2[B_4O_5(OH)_4] \cdot 8H_2O$.
$c$) Trihalides of boron are Lewis bases.

When borax is heated with $CoO$ on a platinum loop,the blue coloured bead formed is largely due to

The structure of diborane $B_2H_6$ is given below. Identify the bond angles $x, y$. In diborane,which bonds are commonly known as banana-bonds?

The general formula of the compounds formed when group $13$ elements $(A)$ react with group $16$ elements $(B)$ is

The incorrect statement regarding '$X$' in the given reaction is $BF_3 + LiAlH_4 \xrightarrow{\text{Ether}} (X) + LiF + AlF_3$.

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Boron is unable to form $BF_{6}^{3-}$.
Reason $R$: Size of $B$ is very small.
In the light of the above statements,choose the correct answer from the options given below.