Which of the following compounds is formed as a blue bead when borax is heated with cobalt oxide?

Which one of the following is the correct statement?

The compound$(s)$ which react$(s)$ with $NH_3$ to give boron nitride $(BN)$ is(are):

In which of the following does the inert pair effect play a significant role?

Explain the following:
$(1)$ Aluminum forms $[AlF_6]^{3-}$ ion but boron does not form $[BF_6]^{3-}$ ion.
$(2)$ $PbX_2$ is more stable than $PbX_4$.

Assertion $(A)$: $[B(OH_2)_6]^{3+}$ and $[B(OH)_4]^{-}$ form octahedral and tetrahedral structures.
Reason $(R)$: Being electron deficient,boron readily reacts with Lewis bases like $H_2O$ and $OH^{-}$.
The correct option among the following is