The hardest substance amongst the following is

For a $p$-block element,its $3d, 3s, 3p$ and $4s$ orbitals are completely filled and the differentiating electron goes to the $4p$ orbital. The element should have its atomic number in the range:

What are the correct statements about the elements of group $13$ given below?
$(I)$ The stability of $+1$ oxidation state follows the order $Tl > In > Ga$
$(II)$ Boron has the lowest melting point and boiling point as it is a non-metal
$(III)$ Boron shows a maximum covalency of $4$ in its compounds
$(IV)$ The order of atomic radius is $Ga > Al > In$
$(V)$ Aluminium is passive to concentrated nitric acid

Identify the correct statements from the following:
$i$. $H_3BO_3$ is a monobasic acid.
$ii$. The correct formula of borax is $Na_2[B_4O_5(OH)_4] \cdot 8H_2O$.
$iii$. $NaBH_4$ is a reducing agent.

Which of the following is responsible for the cleansing action of $Borax$?

Describe the chemical properties of the elements of group $13$.