Question

The ability of a substance to assume two or more crystalline structure is called
(a) Isomerism
(b) Polymorphism.
(c) Isomorphism.
(d) Amorphism.

Answer 1

Hint: The organic compound glycine is exhibiting the phenomenon of polymorphism. It has two polymorphs i.e., hexagonal, and monoclinic crystals.

Complete Step by Step Solution:
Polymorphism
Solid compounds exist in two different crystalline forms.
The polymorph has different physical properties and sometimes chemical properties such as., melting point, color, hardness, solubility, dissolution rate, as well as variance in chemical reactivity.
Isomerism is a type of Polymorphism.
Types of polymorphism
On the bases of the stability of crystalline form, polymorphism can be classified into two types.
Mono-tropic polymorphism
In mono-tropic polymorphism, only one polymorph is stable for all the acceptable temperatures.
E.g., metolazone exhibit such type of polymorphism.
Enantiotropic Polymorphism
In the enantiotropic system of polymorphism, there are different polymorphs, and each polymorph is stable under a specific range of temperatures. Thus, one polymorph is stable at a low temperature, another can be stable at a high-temperature and so on.
E.g., acetazolamide and carbamazepine exhibit this type of polymorphism.
Polymorphism is very useful in pharmaceuticals to enhance the bioavailability and solubility of drugs.
The above explanation shows that (b) is the correct option.

Note: Paracetamol powder has very poor compression properties. It causes difficulties in making tablets; therefore, a new and more compressible polymorph has been found. Cortisone acetate occurs in five separate polymorphs, of which four are soluble in water and can be transformed into a stable shape. Ostwald’s rule states that less stable polymorphs crystallise before the stable form.