What is a characteristic property of acids in organic chemistry?

In organic chemistry, acids are defined by their ability to donate protons (H⁺ ions) in solution, which is a key characteristic of acidic substances. One of the classic indicators of acidity is the behavior of litmus paper. Specifically, acids turn blue litmus paper red, which is a well-established reaction that serves as a simple test for acidic solutions. When the blue litmus comes into contact with an acidic solution, the pH of the solution causes a chemical change in the dye of the litmus, resulting in a color shift that indicates acidity.

This indicator property is widely used in both educational and laboratory settings to quickly assess the acidity of a substance. The other options do not accurately represent characteristics of acids; for instance, a slippery feel and a bitter taste are associated with bases, while the production of oxygen when dissolved in water is not a relevant characteristic of acids. Therefore, the ability of acids to change the color of litmus paper effectively highlights their acidic nature and confirms the validity of selecting the first choice.