Which of the following is not a characteristic of a crystalline solid?
A. Definite and characteristic heat of fusion.

B. Isotropic nature.

C. A regular periodically repeated pattern of arrangement of constituent particles in the entire crystal.

D. A true solid

• Isotropicity (equal values of physical properties) or anisotropicity (unequal values of symmetrical properties) is the property that deals with distribution of inherent physical property( eg. - mechanical strength, refractive index) of any substance to the different molecular axes in accordance with the symmetry of the molecules of that substance.

• Crystalline solids are anisotropic in nature i.e. they show different values of physical properties like electrical resistance or refractive index in different directions, unlike the amorphous solids. This is primarily because of their uneven arrangement of particles in different directions (x, y and z axes). It depends upon the symmetry of the molecules which are arranged in a different way in all the planes (3-dimensional x, y and z planes ).

This figure above shows an example of a simple 2-dimensional arrangement of 2 different types of atoms in a crystal. Here the CD direction row there is 2 types of atoms whereas in AB direction row is made of only one type of atoms – this arrangement will result in anisotropicity and different values for physical properties in different rows of directions.