Which of the following is a characteristic of acids?

Acids are substances that, when dissolved in water, release hydrogen ions (H⁺). One of the most recognizable characteristics of acids is their effect on pH and indicators like litmus paper. In this case, acids will turn blue litmus paper red, which is a classic test for acidity. This color change occurs because the presence of hydrogen ions in the solution alters the chemical structure of the litmus dye, causing a shift from blue to red, demonstrating the acidic nature of the solution.

In contrast, the other characteristics mentioned do not apply to acids. A pH greater than 7 typically indicates a basic or alkaline solution, not an acid. Bitter taste is commonly associated with bases rather than acids, as is the slippery feel that bases have when touched. These differences are important for distinguishing between acidic and basic properties in chemistry.