Q: A crystalline solid

Explanation:

Crystalline Solid Properties

A crystalline solid is characterized by its highly ordered and repeating arrangement of atoms or molecules in a fixed geometric pattern. One of the key properties of crystalline solids is that they have a definite melting point. This means that when a crystalline solid is heated, it remains solid up to a specific temperature. At this precise temperature, the solid abruptly transitions into a liquid state. This sharp change occurs because the regular structure of the crystalline solid breaks down suddenly once the thermal energy overcomes the forces holding the particles in place.

Option B is incorrect because crystalline solids do have a definite melting point. Option C is wrong because crystalline solids do not easily deform; they are typically rigid and maintain their shape until they reach their melting point. Option D is also incorrect because crystalline solids have a regular and orderly three-dimensional arrangement, not an irregular one.

Therefore, the correct answer is that a crystalline solid changes abruptly from solid to liquid when heated.