In the reaction $B_2O_3 + C + Cl_2 \to A + CO$,the $A$ is:

$A$ nonmetallic element of group $13$,used in making bulletproof vests,is an extremely hard solid of black colour. It can exist in many allotropic forms and has an unusually high melting point. Its trifluoride acts as a Lewis acid towards ammonia. The element exhibits a maximum covalence of four. Identify the element and write the reaction of its trifluoride with ammonia. Explain why the trifluoride acts as a Lewis acid.

Discuss the pattern of variation in the oxidation states of $(i)$ $B$ to $Tl$ and $(ii)$ $C$ to $Pb$.

State the uses of aluminium and copper.

Which of the following compounds is formed in the borax bead test?

Which of the following will not give a borax bead test?