Concept:A sharp melting point is a characteristic feature of true crystalline solids, which have a highly ordered, repeating internal structure. Amorphous solids lack this order and melt over a range of temperatures.
Solution:- Diamond is a highly ordered, 3D covalent network crystalline solid. Because all its bonds are identical and ordered, they break at a specific, uniform temperature, yielding a very sharp melting point.
Why other options are incorrect:- B, C: Glass and coal tar are classic examples of amorphous solids; they soften gradually over a range of temperatures rather than melting sharply.
- A: While some gemstones are crystalline, "gemstone" is a generic term that can include amorphous materials like opal or amber. Diamond is the specifically stated crystalline solid.
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