Crystalline solids possess $......$.

Which one of the following elements, when present as an impurity in silicon, makes it a $p$-type semiconductor?

Amorphous solids are......

What is the main use of $Quartz$?

What type of semiconductor is obtained by doping $Ge$ with $As$ $(P, Sb, Bi)$?

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.