Concept:Melting and boiling points are characteristic physical properties that differ from one pure substance to another.
Explanation:The melting point is the temperature at which a solid changes to a liquid.
The boiling point is the temperature at which a liquid changes to a gas.
Both temperatures depend on the strength of intermolecular forces and the molecular structure of the substance.
Since different pure substances have different forces and structures, their melting and boiling points are not fixed across all substances.
Instead, these values vary from substance to substance.
Answer:D. The melting and boiling points can vary depending on the substance.