What is defined as a reaction in which solids form upon the interaction of two solutions?

A reaction in which solids form upon the interaction of two solutions is characterized as a precipitation reaction. In this type of reaction, when two soluble compounds are mixed in solution, they can react to form an insoluble compound, known as a precipitate, which then separates from the solution as a solid. This solid can often be seen as a ‘cloudy’ or ‘turbid’ formation in the mixture.

Precipitation reactions are commonly used to identify the presence of certain ions in solution, where specific combinations lead to the formation of compounds that are responsible for the cloudy appearance. For instance, if you mix solutions of silver nitrate and sodium chloride, you would observe the formation of silver chloride, which appears as a white precipitate.

The other types of reactions listed — combustion, oxidation, and synthesis — do not specifically involve the formation of solids in the way that precipitation reactions do. Combustion involves the reaction of a substance with oxygen, oxidation concerns the transfer of electrons and changes in oxidation states, and synthesis refers to the combination of two or more materials to form a more complex product. Each of these has distinct characteristics that separate them from the nature of precipitation reactions.