Question

The changing of substances from liquid to solid is referred to as:
A. Melting
B. Freezing
C. Liquefaction
D. Both A and C

Answer 1

Hint: Two of the given options refer to a process in which the state of matter of the substance changes from solid to liquid while only one process refers to the process where it changes from solid to liquid. With this information, try and work out the answer to the given question.

Step-by-Step Solution:
To help us solve this question, let us go through each of the concepts given in the options one at a time and then pick the most suitable one of the three.
1. Starting with the process of melting, also known as fusion, it is a physical process that results in the phase transition of a substance from a solid to a liquid.
2. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which increases the substance's temperature to the melting point. At the melting point, the ordering of ions or molecules in the solid breaks down to a less ordered state, and the solid melts to become a liquid.
3. Let us now move on to the process of freezing, it is a phase transition where a liquid changes to a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid or the liquid content of a substance, usually due to cooling.
4. Finally, let us now talk about the process of liquefaction. It is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of the latter, an application of liquefaction is the liquefaction of air to allow separation of the constituents, such as oxygen, nitrogen, and the noble gases. Another is the conversion of solid coal into a liquid form usable as a substitute for liquid fuels.
Through this analysis, we can safely conclude that the answer to this question is b) Freezing.

Note: Remember that while liquefaction can cause a phase change from gases to liquids, this does not satisfy the required criteria and can therefore not be the answer. Also, be very wary of the difference between freezing and melting as they involve opposite phase changes at the same temperature.