Here's why:

* pH Scale: The pH scale measures acidity and alkalinity. A pH of 7 is neutral (like pure water). Values below 7 are acidic, and values above 7 are basic (alkaline).

* 7 Up's pH: The exact pH of 7 Up can vary slightly depending on the specific formulation, but it's generally around 3.0 to 4.0.

* Citric Acid: 7 Up contains citric acid, which contributes to its slightly acidic nature. Citric acid is a weak acid found naturally in citrus fruits.

While 7 Up is acidic, it's not considered a strong acid. Its acidity is relatively mild compared to substances like vinegar or lemon juice.