Giant covalent structures feature extended lattices of covalently bonded atoms

Steps:

• Define giant covalent structure as a three-dimensional network of strong covalent bonds between atoms, like in diamond or silica.
• Identify each substance's bonding type at room temperature.
• Match the definition to the option with an extended covalent network.
• Confirm sand's composition as silicon dioxide (SiO₂), which fits the structure.

Why B is correct:

• Sand is primarily SiO₂, forming a giant covalent lattice where silicon and oxygen atoms are linked by covalent bonds in a tetrahedral network, per the structure of quartz.

Why the others are wrong:

• A. Methane (CH₄) consists of discrete molecules held by weak intermolecular forces, not a giant covalent network.
• C. Sodium chloride (NaCl) has an ionic lattice with electrostatic attractions between Na⁺ and Cl⁻ ions.
• D. Water (H₂O) forms simple molecular structures with hydrogen bonds between discrete molecules.

Final answer: B