Which of the following solids would have the highest melting point?

• A. Sodium chloride (NaCl)
• B. Solid carbon dioxide (CO_2)
• C. Ice (H_2O)
• D. Iodine (I_2)

Answer: (A)

Verified step by step guidance

1. Identify the types of intermolecular or interionic forces present in each solid: Sodium chloride (NaCl) is an ionic solid, solid carbon dioxide (CO_2) is a molecular solid with London dispersion forces, ice (H_2O) is a molecular solid with hydrogen bonding, and iodine (I_2) is a molecular solid with London dispersion forces.
2. Recall that ionic solids like NaCl have strong electrostatic attractions between ions, which generally result in much higher melting points compared to molecular solids.
3. Understand that molecular solids held together by hydrogen bonds (like ice) have higher melting points than those held only by London dispersion forces (like CO_2 and I_2), but still lower than ionic solids.
4. Compare the relative strengths of these forces: ionic bonds > hydrogen bonds > London dispersion forces, which helps predict the order of melting points.
5. Conclude that because NaCl is held together by strong ionic bonds, it will have the highest melting point among the given solids.