Borax dissolves in water and forms a product of boron $(X)$. Identify the compound $X$.

$A$ Lewis acid '$X$' reacts with $LiAlH_{4}$ in ether medium to give a highly toxic gas. This gas when heated with $NH_{3}$ gives a compound commonly known as inorganic benzene. The gas is

Which of the following reactions is used to prepare borazine?

$TlI_3$ is isomorphous with:

Given below are two statements:
Statement $I$: Boron is extremely hard,indicating its high lattice energy.
Statement $II$: Boron has the highest melting and boiling point compared to its other group members.
In the light of the above statements,choose the most appropriate answer from the options given below:

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