Pure silicon doped with phosphorus is

What is the main use of $Quartz$?

The ability of a substance to assume two or more crystalline structures is called

To prepare $p$-type semiconductors,which type of impurity is added to intrinsic semiconductors?

Given below are two statements. One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Sharp glass edge becomes smooth on heating it up to its melting point.
Reason $R$: The viscosity of glass decreases on melting.
Choose the most appropriate answer from the options given below.

Match the column $A$ (type of crystalline solid) with the column $B$ (example for each type).

$P$. Molecular solid	$i$. $SiC$
$Q$. Ionic solid	$ii$. $Mg$
$R$. Metallic solid	$iii$. $H_2O$
$S$. Network solid	$iv$. $MgO$