States of Matter

Ethanol has the lowest melting point. Iron has the highest boiling point.

These results can be directly inferred from the values in the table: the substance with the lowest melting point changes from solid to liquid more easily (at a lower temperature), while the substance with the highest boiling point requires the most heat to change into a gas.

For each substance in the table, the melting point equals the freezing point.

For pure substances, the melting and freezing points are the same — the solid ↔ liquid equilibrium occurs at a single temperature. This shows that phase changes in pure substances take place at a specific and constant temperature (also depending on external pressure). Mixtures or solutions can alter this behavior, causing melting/freezing to occur over a range of temperatures.

First phase change: Mercury melts from solid to liquid because, with a melting point of 46°C, it is the solid with the lowest melting temperature above 20°C — when it reaches 46°C, the vibration energy of its particles is enough to overcome the solid bonds and become fluid.

Last phase change: Iron changes last; its melting (1538°C) and boiling points (2862°C) are very high. If by “last” we mean the final phase change in the entire process (vaporization), then iron’s boiling at 2862°C occurs last.

Ethanol (melting point 0°C, boiling point 100°C): Liquid. (0°C < 25°C < 100°C)

Mercury (melting point 46°C): Solid. (25°C < 46°C → has not melted) — (Note: this is according to the given table)

Sodium chloride (melting point 801°C): Solid. (25°C is much lower)

Iron (melting point 1538°C): Solid. (25°C is much lower)

The physical state of a substance at a given temperature is determined by comparing the temperature with its melting (solid → liquid) and boiling (liquid → gas) points. If the temperature is below the melting point, the substance is solid; if it is between the melting and boiling points, it is liquid; if it is above the boiling point, it is gas.