Question

Which of the following is amorphous?
A.Sodium chloride
B.Quartz glass
C.Powdered marble
D.Cane sugar

Answer 1

An amorphous solid is any non-crystalline solid in which the atoms and molecules are not organized in a definite pattern. They are mostly covalently bonded and do not have any sharp melting point.

Complete step by step answer:
Amorphous solids do not have any definite ordered structure. They do not have a sharp melting point. They have no characteristic heat of fusion and are isotropic, i.e. have similar properties in all directions. They are mostly covalently bonded.
In option A, sodium chloride is an ionic compound with a sharp melting point at ${\rm{80}}{{\rm{0}}^o}C$. The lattice of sodium chloride is arranged such that the atoms are present alternatively in all directions. So, sodium chloride is a crystalline solid.
In option B, quartz glass is a type of glass consisting of silica. It is produced by melting quartz in a vacuum or at very high temperatures. The melting point of quartz is approximately ${\rm{160}}{{\rm{0}}^o}C$. Thus, quartz glass is an amorphous solid.
In option C, powdered marble is produced as a waste product during the production of marble. It can also be used as filler material in cement. Though it is in powdered form, the composition of marble remains the same i.e. ${\rm{CaC}}{{\rm{O}}_3}$. It has a definite structure and a melting point of ${\rm{134}}{{\rm{0}}^o}C$. Thus, it is a crystalline compound.
In option D, cane sugar as we know is just sucrose extracted from sugarcane. It is made up of glucose and fructose molecules attached by 1, 4 linkage alternatively. It also has a sharp melting point of ${\rm{18}}{{\rm{6}}^o}C$ . Thus, cane sugar is also crystalline.

$\therefore$ The correct option is option B, i.e. quartz glass.

Note:
Amorphous solids are sometimes also called as super-dense liquids due to their characteristics. Some main examples of amorphous solids are gels, thin films, glass etc. They are also highly soluble and are preferred in pharmaceuticals. They have higher tensile strength than crystalline solids and do not break easily as well.