Which of the following must occur in order to melt NaCl (sodium chloride)?

• A. Heat the NaCl to a temperature above its melting point so the ionic bonds are overcome.
• B. React NaCl with hydrochloric acid to produce a liquid.
• C. Expose NaCl to ultraviolet light to break its chemical bonds.
• D. Add water to dissolve the NaCl at room temperature.

Answer: (A)

Verified step by step guidance

1. Understand that melting a solid like NaCl involves changing its physical state from solid to liquid by overcoming the forces holding its ions together, which are ionic bonds.
2. Recall that ionic bonds in NaCl are strong electrostatic attractions between Na⁺ and Cl⁻ ions arranged in a crystal lattice, requiring significant energy to break.
3. Recognize that melting occurs when the substance is heated to its melting point, providing enough thermal energy to overcome these ionic bonds without breaking the chemical identity of the compound.
4. Note that reacting NaCl with hydrochloric acid or exposing it to ultraviolet light involves chemical changes or bond breaking, not simply melting, and adding water dissolves NaCl rather than melting it.
5. Conclude that the correct process to melt NaCl is to heat it above its melting point so the ionic bonds are overcome, allowing the solid to become liquid.