$A{l_2}{O_3}$ formation involves evolution of a large quantity of heat, which makes its use in

Explain the following:

$(1)$ $Tl (NO_3)_2$ acts as an oxidizing agent.

$(2)$ Carbon shows catenation property but lead does not. 

$STATEMENT$-$1$: In water, orthoboric acid behaves as a weak monobasic acid. because

$STATEMENT$-$2$: In water, orthoboric acid acts as a proton donor.

What happens when...

$(a)$ Borax is heated strongly,

$(b)$ Boric acid is added to water,

$(c)$ Aluminium is treated with dilute $NaOH,$

$(d) $ $B F_3$ is reacted with ammonia ? 

When metal $X$ is treated with sodium hydroxide, a white precipitate $(A)$ is obtained, which is soluble in excess of $NaOH$ to give soluble complex $(B)$. Compound $(A)$ is soluble in dilute $HCl$ to form compound $(C)$. The compound $(A)$ when heated strongly gives $(D)$, which is used to extract metal. Identify $(X), (A), (B), (C)$ and $(D)$. Write  suitable equations to support their identities. 

The weakest Lewis acid is