Solid NaCl is:

A. amorphous
B. crystalline
C. anisotropic
D. isotropic

Choose the correct answer from the options given below:

B & C only

The correct answer is Option (3) → B & C only.

Solid NaCl (sodium chloride) is a crystalline ionic solid with a regular and ordered structure, and its physical properties vary depending on the direction in which they are measured. Let us break down the details to explain why NaCl is crystalline and anisotropic, and why it is not amorphous or isotropic.

Crystalline Nature of NaCl:

Crystalline solids are characterized by a regular, repeating pattern of atoms, ions, or molecules in three dimensions. In NaCl, sodium ions (Na⁺) and chloride ions (Cl⁻) are arranged in a well-defined crystal lattice, known as a face-centered cubic (FCC) structure.

The structure of crystalline NaCl is highly ordered. Each Na⁺ ion is surrounded by six Cl⁻ ions, and each Cl⁻ ion is surrounded by six Na⁺ ions. This repeating arrangement extends throughout the entire solid, forming a crystal lattice.

Crystalline solids have sharp melting points and specific geometrical shapes, which differentiate them from amorphous solids (discussed below).

Anisotropic Nature of NaCl:

Anisotropy means that a material exhibits different physical properties when measured along different directions. In NaCl, properties like refractive index, electrical conductivity, and mechanical strength can vary depending on the direction in the crystal lattice.

This occurs because the ions are arranged in specific planes and directions. For instance, the ionic bonds and distances between ions might cause NaCl to conduct electricity more easily in one direction than another. This directional dependence of properties is characteristic of anisotropic materials.

Crystalline solids, by their very nature, tend to be anisotropic because of their ordered, directional arrangement of particles.

NaCl is Not Amorphous:

Amorphous solids, in contrast to crystalline solids, do not have a long-range repeating order of particles. Examples of amorphous materials include glass and plastic, where atoms are arranged randomly and there is no specific pattern over long distances.

Since NaCl has a highly organized crystal structure, it is not amorphous. Amorphous solids generally do not have sharp melting points and are isotropic (discussed below), unlike NaCl

NaCl is Not Isotropic:

Isotropy refers to having identical physical properties in all directions. Amorphous solids are typically isotropic because their particles are arranged randomly and uniformly throughout the material. This lack of ordered structure leads to identical properties in every direction.

NaCl, however, is not isotropic because its properties vary based on the orientation within the crystal lattice. As a result, NaCl is anisotropic rather than isotropic.

Summary of Options:

A. Amorphous: NaCl is not amorphous because it has a well-defined, repeating crystalline structure.

B. Crystalline: NaCl is crystalline due to its ordered lattice arrangement.

C. Anisotropic: NaCl is anisotropic because its physical properties vary along different directions in the crystal.

D. Isotropic: NaCl is not isotropic because its properties change based on the direction in the lattice.