In which of the following substances are the atoms held together by metallic bonding?

• A. Water (H_2O)
• B. Sodium chloride (NaCl)
• C. Copper (Cu)
• D. Carbon dioxide (CO_2)

Answer: (C)

Verified step by step guidance

1. Understand the nature of metallic bonding: Metallic bonding occurs between metal atoms where valence electrons are delocalized and shared in a 'sea of electrons' that holds the metal atoms together.
2. Analyze Water (H_2O): Water molecules are held together by covalent bonds between hydrogen and oxygen atoms, and intermolecular hydrogen bonds, not metallic bonds.
3. Analyze Sodium chloride (NaCl): Sodium chloride is an ionic compound where positively charged sodium ions and negatively charged chloride ions are held together by ionic bonds, not metallic bonds.
4. Analyze Copper (Cu): Copper is a metal, and its atoms are held together by metallic bonding, characterized by a lattice of metal cations surrounded by a sea of delocalized electrons.
5. Analyze Carbon dioxide (CO_2): Carbon dioxide molecules are held together by covalent bonds between carbon and oxygen atoms, with intermolecular forces between molecules, not metallic bonds.