Question

What are the two types of solids?

Answer 1

1. Solids are substances having fixed shape, size and volume. They are characterised by incompressibility, rigidity and mechanical strength.
2. The atoms/molecules/ions of a solid are held together by strong cohesive forces and cannot move randomly. Thus, the atomic/ionic/molecular arrangement of solids is regular and well ordered.
3. Solids are of two types, crystalline and amorphous. Their characteristics are given below

Crystalline solids	Amorphous solids
Crystalline solids have a definite and orderly arrangement of atoms/molecules/ions in 3D space. Due to this, they have a definite and regular geometry. Thus, crystalline solids are said to have long-range order.	Amorphous solids, on the other hand, do not have any pattern of arrangement of atoms/molecules/ions in 3D space. Therefore, they do not have any definite geometrical shape. Thus, amorphous solids do not have long-range order.
Crystalline solids have a sharp melting point.	Amorphous solids do not have a sharp melting point. Hence, amorphous solids are considered to be “liquids at all temperatures”.
Properties such as electrical and thermal conductivity, mechanical strength and refractive index are different in different directions. Crystalline solids are said to be anisotropic.	Properties such as electrical and thermal conductivity, mechanical strength and refractive index are the same in all directions. Amorphous solids are thus said to be isotropic.
Examples: Diamond, Sodium chloride ($\mathrm{NaCl}$) crystals, Sugar crystals etc.	Examples: Glass, Rubber etc.

4. Final Statement: Solids are of two types, crystalline and amorphous.