Answer:
The correct answer is "formation of a precipitate".
Step-by-step explanation:
The boiling, melting and freezing reactions are physical reactions since they are produced by the increase or decrease of the temperature and do not present changes in the chemical composition. Precipitation reactions take place when a non-soluble compound is formed which is called "precipitate", which is generated by mixing two different solutions.
A precipitation reaction occurs when one or more reagents, combining to generate an insoluble product that precipitates and is visibly appreciable.
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