Which beverage would likely be categorized as an acid during the students' investigation?

Orange juice is classified as an acid primarily because it contains citric acid, which contributes to its tangy flavor and acidic properties. The pH of orange juice is typically in the range of 3 to 4, making it distinctly acidic. In the context of a classroom investigation where students are identifying substances based on their pH levels, comparable experiments would demonstrate that beverages with lower pH values are more acidic.

In contrast, milk is neutral to mildly acidic, often hovering around a pH of 6 to 7, while water is neutral at a pH of 7. Ammonia, on the other hand, is a base with a high pH, making it alkaline rather than acidic. Therefore, among the choices provided, orange juice stands out as the clear example of an acidic beverage because of its citric acid content and lower pH.