Question

Which of the following is the non-crystalline solid?
A.$CsCl$
B.$NaCl$
C.$Ca{F_2}$
D.$Glass$

Answer 1

First we should be aware of the term non-crystalline solids and what they actually represent and as a group they are. Then we have to define their physical properties and the differences with the crystals so that we can get the proper points to distinguish between the options. Then we get the answer by observing the structure of the given options in which all others are specific lattices apart from one.

Complete step by step answer:
In the case of condensed matter physics and materials science, an amorphous solid is a solid that lacks the long-range order that is characteristic of a crystal. That means that the lattice isn’t arranged specifically in an order. Lattice points don’t repeat themselves like they do in crystals and its structure is all random.
These amorphous solids are also called non-crystalline solids. They are just another name given to the solids of this kind.
There are many differences between the amorphous and crystalline solids. Like :
Lattice structure
The characteristic shape
The difference between the melting and the boiling points.
$CsCl$,$NaCl$, and $CaF_2$ are all ionic compounds and are crystalline in nature. They all have specific lattice blocks and lattice structures in their bonding. Whereas, Glass is amorphous solid as it doesn't possess a well developed perfectly ordered crystalline structure.
Therefore the answer is the option D, Glass.

Note:
Non-crystalline solids are pseudo solids or super cooled liquids. In many cases they are defined as developed solids through the process of cooling. They do not have sharp melting points. They are isotropic in nature.