The Lewis acid nature of $BX_3$ follows the order:

State the uses of aluminium and copper.

Write the chemical reaction of $Al$ with aqueous alkali.

The correct statements from the following are $:$
$(A)$ $Tl^{3+}$ is a powerful oxidising agent
$(B)$ $Al^{3+}$ does not get reduced easily
$(C)$ Both $Al^{3+}$ and $Tl^{3+}$ are very stable in solution
$(D)$ $Tl^{+}$ is more stable than $Tl^{3+}$
$(E)$ $Al^{3+}$ and $Tl^{+}$ are highly stable
Choose the correct answer from the options given below $:$

When orthoboric acid $(H_3BO_3)$ is heated,the residue left is:

Give important trends and anomalous properties of boron.