Final answer:
The melting point of a substance remains constant, regardless of the sample size because it is an intrinsic property determined by the substance's intermolecular forces.
Step-by-step explanation:
The melting point of a sample will stay the same when the size of the sample increases. This property does not depend on the quantity of the material. Instead, the melting point is an intrinsic property of a substance that is determined by the specific interactions between its particles, such as ionic bonds, covalent bonds, metallic bonds, hydrogen bonds, Van der Waals forces, etc. Therefore, regardless of whether you have a small or large amount of a substance, the temperature at which it changes from a solid to a liquid remains constant under constant pressure.
For example, water will always have a melting point of 0°C (32°F) at 1 atmosphere of pressure, irrespective of whether you have a glass of ice or an iceberg. Similarly, a metal like iron melts at 1538°C, regardless of the amount you have. This principle also applies to other substances with different types of intermolecular forces.