Which of the following substances has a pH of about 3?

The substance that has a pH of about 3 is oranges. Oranges are citrus fruits that contain citric acid, contributing to their acidic nature and giving them a pH value typically in the range of 3 to 4. This acidity is responsible for their tart flavor and is a common characteristic of many citrus fruits.

In contrast, apples generally possess a pH closer to neutral, usually between 3 and 4 but often slightly higher than that of oranges. Milk has a pH around 6 to 7, making it neutral or mildly acidic, while pure water has a neutral pH of 7. The significant difference in pH values among these substances highlights the importance of acidity in classifying foods and their taste profiles.