Crystalline solids are the type of solid structure that melts at a definite, sharp melting point.

Crystalline solids have a highly ordered and regular arrangement of atoms, ions, or molecules in a three-dimensional lattice structure. This arrangement gives rise to a well-defined and repeating pattern of particles, resulting in a characteristic shape and sharp melting point.

Explanation:
Crystalline solids are characterized by their long-range order and periodic arrangement of constituent particles. This means that the atoms, ions, or molecules in a crystalline solid are arranged in a repeating pattern throughout the entire solid. This regular arrangement allows for strong intermolecular forces between particles, resulting in a high degree of structural stability.

When a crystalline solid is heated, the thermal energy supplied to the solid causes the particles to vibrate more vigorously. As the temperature continues to rise, the particles gain enough energy to overcome the intermolecular forces holding them in place, and the solid begins to melt.

The melting process of a crystalline solid occurs abruptly at a specific temperature, known as the melting point. At this temperature, the intermolecular forces are weakened to the point where the solid transitions into a liquid state. The melting point is a unique characteristic property of a substance and remains constant as long as the pressure is constant.

The sharp melting point of crystalline solids is a result of the regular arrangement of particles and the uniform strength of intermolecular forces throughout the lattice. Each particle in the crystal lattice experiences similar forces from its neighboring particles, leading to a consistent energy requirement for melting.

In contrast, amorphous solids do not possess a well-defined and ordered lattice structure. The arrangement of particles in amorphous solids is more random and lacks long-range order. As a result, amorphous solids do not have a sharp melting point but rather soften gradually over a range of temperatures. The absence of a specific melting point in amorphous solids is due to the varying strength of intermolecular forces within the material.

In conclusion, crystalline solids exhibit a distinct and sharp melting point due to their highly ordered lattice structure and uniform intermolecular forces. This characteristic property allows for precise control over melting and solidification processes, making crystalline solids valuable in various applications, such as materials science, chemistry, and engineering.