Giant covalent structures feature extended 3D networks of covalent bonds

Steps:

• Recall giant covalent structures consist of atoms linked by covalent bonds in a continuous lattice, like diamond or silicon dioxide.
• Analyze methane: CH4 forms discrete molecules with weak van der Waals forces, not a lattice.
• Analyze sand: SiO2 has silicon and oxygen atoms in a tetrahedral covalent network extending infinitely.
• Analyze sodium chloride and water: NaCl is ionic with oppositely charged ions; H2O is molecular with hydrogen bonds between separate units.

Why B is correct:

• Sand is silicon dioxide (SiO2), where each silicon bonds covalently to four oxygens in a giant tetrahedral lattice, per the structure of quartz.

Why the others are wrong:

• A: Methane is a simple molecular compound with isolated CH4 molecules held by weak forces.
• C: Sodium chloride forms a giant ionic lattice of Na+ and Cl- ions attracted electrostatically.
• D: Water consists of discrete H2O molecules linked by hydrogen bonds, not covalent networks.

Final answer: B