Concept:The heat of fusion is the energy required to melt a solid. Pure crystalline ionic compounds have highly specific, sharply defined melting points and characteristic heats of fusion.
Solution:- Note on Exam Fidelity: The test makers flagged this question conceptually. However, the intended logic separates simple ionic lattices from massive covalent networks.
- \( NaCl \), Aluminium Oxide, and Iron Oxide are crystalline ionic lattices that undergo a standard, sharp phase transition from solid to liquid, yielding a precise characteristic heat of fusion.
- Silicates (like glass or quartz) often exist as giant continuous covalent networks or amorphous solids. Amorphous silicates do not have a sharp melting point; they gradually soften over a wide temperature range, meaning they lack a single characteristic heat of fusion.
Why other options are incorrect:Options A, B, and C are simple crystalline ionic solids with precise, easily measured heats of fusion.
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