Which of the following is a network solid?

Correct option is C

A network solid or covalent network solid (also called atomic crystalline solids or giant covalent structures) is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal or amorphous solid may be considered a macromolecule. These solids are usually hard and have high melting points.
Examples of network solids include diamond with a continuous network of carbon atoms and silicon dioxide or quartz with a continuous three-dimensional network of SiO2 units. 
Among the given options:
· CCl₄ (a) is a molecular solid with covalent bonds within molecules.
· NaCl (b) is an ionic solid, formed by the electrostatic attraction between Na⁺ and Cl⁻ ions.
Additional Knowledge:
(a) CCl₄:
· Carbon tetrachloride is a simple molecular solid.
· Commonly used as a solvent and in fire extinguishers.
(b) NaCl:
· Sodium chloride is an ionic solid with a lattice structure.
· Composed of alternating Na⁺ and Cl⁻ ions held by ionic bonds.
· It dissolves readily in water and conducts electricity in molten or aqueous form.
(c) SiO₂:
· Quartz (SiO₂) is a classic example of a covalent network solid.
· It forms a continuous tetrahedral lattice of silicon and oxygen atoms.