Crystalline solids have a highly ordered structure, resulting in a sharp, definite melting point due to uniform energy requirements for breaking bonds.

Amorphous solids, like glass, lack long-range order, leading to a random particle arrangement, unlike crystalline solids.

Diamond’s strong covalent network structure, with each carbon bonded to four others, requires significant energy to break, resulting in a very high melting point.

In a BCC unit cell, each atom is surrounded by 8 nearest neighbors, defining its coordination number.

Metallic solids conduct electricity due to the presence of free electrons in their delocalized electron sea.

FCC lattices have the highest packing efficiency among cubic structures, at 74%, due to close packing of atoms.

Schottky defects involve vacancies of equal numbers of cations and anions, common in ionic solids like NaCl where ion sizes are similar.

Dry ice (solid CO2) is a molecular solid held together by weak van der Waals forces between CO2 molecules.

A simple cubic unit cell has 8 atoms at the corners, each contributing 1/8, so total atoms = 8 × 1/8 = 1.

Ionic solids are brittle because strong electrostatic forces between ions resist deformation, causing cleavage upon stress.

Frenkel defect occurs when a smaller ion (usually cation) occupies an interstitial site, leaving a vacancy, common in ionic solids with size disparity.

Naphthalene, a molecular solid, has weak van der Waals forces, leading to a low melting point and soft texture.

Diamond has a covalent network structure with each carbon atom covalently bonded to four others in a tetrahedral arrangement.

Metallic solids conduct electricity in the solid state due to free electrons, unlike ionic solids, which conduct only when molten or dissolved.

A simple cubic unit cell has atoms only at the eight corners, contributing 1/8 each, totaling 1 atom per unit cell.

Interstitial defects involve extra atoms in interstitial sites, adding mass without increasing volume, thus increasing the crystal’s density.

Graphite has a layered covalent network structure with strong C-C covalent bonds within layers and weak van der Waals forces between layers.

FCC and HCP lattices both have a coordination number of 12, the highest among common lattices; FCC is the correct choice here.

Ionic solids conduct electricity only when molten or dissolved, not in the solid state, due to fixed ion positions.

CsCl has a BCC-like structure with one ion at the center and eight of the opposite ion at the corners, resembling a body-centered cubic lattice.