Write the name of any four types of glasses.

Fill in the blank with a suitable word:

Stained glass is made by adding different _____ (metals/ chemicals) to the mixture from which glass is made.   

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

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

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.