Which one of the following substances would have the lowest magnitude for the heat of fusion?

• A. Iron (Fe)
• B. Water (H2O)
• C. Mercury (Hg)
• D. Sodium chloride (NaCl)

Answer: (C)

Verified step by step guidance

1. Understand that the heat of fusion is the amount of energy required to change a substance from solid to liquid at its melting point without changing its temperature.
2. Recognize that the heat of fusion depends on the strength of the forces holding the particles together in the solid phase; stronger forces require more energy to overcome.
3. Consider the types of bonding and intermolecular forces in each substance: Iron (Fe) and Sodium chloride (NaCl) have strong metallic and ionic bonds respectively, which generally result in high heats of fusion.
4. Water (H2O) has hydrogen bonding, which is strong among molecular forces, leading to a relatively high heat of fusion compared to substances with weaker forces.
5. Mercury (Hg) is a metal with relatively weak metallic bonding compared to iron and has a low melting point, so it requires less energy to melt, resulting in the lowest magnitude of heat of fusion among the options.