For manufacturing of glass, which among the following is used as a source of silica?

Reinforced glass is a type of safety glass that withstands:

Which of the statements about glass are correct?

$\mathrm{I}$. Glass is a supercooled liquid having infinite viscosity.

$\mathrm{II}$. Violet coloured glass is obtained by adding ${\mathrm{MnO}}_2$.

$\mathrm{III}$. Glass is a man made silicate.

$\mathrm{IV}$. Glass is a crystalline substance.

Select the correct answer using the codes given below.

Statement $\mathrm{I}$: Glass is not considered as a true solid.

Statement $\mathrm{II}$: Glass does not have a definite melting point.