Final answer:
The glass of root beer is a homogeneous mixture, while the other options are heterogeneous mixtures.
Step-by-step explanation:
A homogeneous mixture, also known as a solution, is a mixture that appears uniform throughout. In this case, the glass of root beer is a homogeneous mixture. It consists of carbonated water, flavorings, and sweeteners that are completely and evenly mixed together. The other options, crunchy peanut butter, pepperoni and mushroom pizza, and macaroni and cheese, are examples of heterogeneous mixtures, where the different components can be visually distinguished.