Final answer:
The mixing of two liquids is not always a sign of a chemical reaction; such mixing can simply result in a physical mixture without any chemical change. For a chemical reaction to be present, there must be evidence of a new substance being formed.
Step-by-step explanation:
The statement that the mixing of two liquids is a common sign of a chemical reaction is false. Not all mixtures of liquids result in a chemical reaction; in many cases, they simply form a physical mixture without altering the chemical properties of the components. For instance, when oil and water are mixed, they do not react chemically; they form separate layers because they are not miscible. A chemical reaction involves the breaking and forming of chemical bonds resulting in the production of one or more new substances with different properties from the original substances. Common signs of a chemical reaction include a change of color, production of a gas, formation of a precipitate, and/or a transfer of energy, such as the production of heat or light. Simply mixing two liquid substances does not guarantee a reaction will take place.