Which of the following substances is NOT a network solid?

• A. SiO_2 (quartz)
• B. NaCl (sodium chloride)
• C. C (diamond)
• D. SiC (silicon carbide)

Answer: (B)

Verified step by step guidance

1. Understand what a network solid is: A network solid is a type of solid where atoms are bonded covalently in a continuous three-dimensional network, resulting in very high melting points and hardness.
2. Identify the bonding type in each substance: SiO_2 (quartz), C (diamond), and SiC (silicon carbide) all have covalent bonds forming extended networks, making them network solids.
3. Recognize that NaCl (sodium chloride) is an ionic compound composed of positive and negative ions held together by ionic bonds in a lattice, not covalent bonds.
4. Conclude that because NaCl is held together by ionic bonds rather than a covalent network, it is not classified as a network solid.
5. Therefore, among the given options, NaCl is the substance that is NOT a network solid.