Question

When a mixture of sodium carbonate and calcium carbonate is fused with silica at $$1500^0C$$, a liquid consisting of sodium and calcium is formed. When this liquid is cooled, it becomes various and eventually ceases to flow. It becomes solid and called glass. By varying the proportions of the three basic ingredients and by adding other substances, the properties of glass can be altered. An approximate formula for ordinary glass may be given as,
$$R_2O-MO-65SiO_2$$
Where $$R=Na$$ or $$K$$ and $$M=Ca, Ba, Zn$$ and $$Pb$$

$$SiO_2$$ may be replaced by $$Al_2O_3, B_2O_3, P_2O_5$$. Coloured glasses are obtained by adding certain metallic oxides or salts in the fused mass. Glass is attacked by $$HF$$ and this property is used to make marking on the glass. This is known as etching.
The glass if cooled rapidly becomes brittle and fragile. The articles of glass are cooled neither very slowly nor very rapidly. The articles are cooled gradually. This process it terms annealing.

Glass is described as a :

Answer 1

Correct option is C. super cooled liquid