Due to irregularity in structure, average of physical properties like density, rmal and electrical conductivity etc. is same along any direction for a particular amorphous solid.

Consider atom at body center. It is touched by all atoms present at vertices of cubic unit cell. We know that a cube has 8 vertices.

Mass of an ideal FCC metallic crystal unit cell is four times atomic mass of metal since re are four atoms per unit cell.

Graphite crystals consist of several planar layers of Carbon atoms arranged in interconnected hexagonal rings. Each atom makes three &sigma bonds and one &pi bond. VSEPR ory predicts a trigonal planar molecular structure with respect to each Carbon atom.

Coordination number of a crystal structure is number of particles with which a given particle is in direct contact.

Grain boundaries are regions that separate two grains in polycrystalline metallic solids. The absence of properly defined structure results in residual stresses. Hence, grain boundaries are weak spots in structure and are often site of a fracture.

Unit cell is smallest unit of a crystal which repeats itself to generate crystal. Lattice point represents centres of atoms in a unit cell. Crystal lattice refers to entire structure of a crystalline solid.

Anisotropy is a characteristic behavior shown by ideal crystals. However, presence of flaws like grain boundaries causes solid to deviate from crystalline properties.

Void fraction = 1 − packing efficiency
Since primitive cubic unit cell has least packing efficiency out of those mentioned above, hence it has highest void fraction of (1 − 0.52 = ) 0.48 or 48 %.

Packing efficiency represents fraction of unit cell volume that is utilized to hold particles.