What is a characteristic property of acids?

A characteristic property of acids is that they have a sour taste and turn litmus paper red. This is due to the presence of hydrogen ions (H⁺) in acids, which is responsible for their acidity. The sour taste is something commonly associated with acidic substances such as vinegar (acetic acid) or citrus fruits (like lemons and oranges, which contain citric acid).

Turning litmus paper red is a classic test for acidity. Litmus is a natural dye from lichens that changes color depending on the pH of the solution; it turns red in acidic environments (pH below 7) and blue in basic (alkaline) environments (pH above 7). This property of acids is widely utilized in acid-base chemistry to quickly determine whether a solution is acidic or not.

In contrast, the other options describe properties that do not align with the behavior of acids, such as sweet taste or high pH values, both of which are more characteristic of bases.