Which of the following is an example of a homogeneous mixture?

• A. Vinegar
• B. Soil and gravel
• C. Oil and water
• D. Rice in cereal

Answer: (A)

A homogeneous mixture has the same composition throughout; it forms a single phase where the components are uniformly distributed at the molecular level. Vinegar is a true solution of acetic acid in water, so the mixture is uniform everywhere you sample it—the acetic acid and water are dissolved and no separate parts are visible. In contrast, oil and water do not mix and separate into layers, so the mixture is not uniform. Soil and gravel contain visibly different parts that you can distinguish, which makes it heterogeneous. Rice in cereal also presents distinct components (grains versus cereal) and does not have a uniform composition throughout.