The correct option is **B. It donates protons (H⁺) to the solution.** ### Detailed Explanation: 1. **Understanding Acids:** - In chemistry, acids are defined by their ability to donate protons (H⁺ ions) when dissolved in water. This definition is based on the Brønsted-Lowry theory of acids and bases, which states that an acid is a substance that can donate a proton to another substance (the base). 2. **Behavior in Aqueous Solution:** - When an acid is added to water, it dissociates (breaks apart) to release H⁺ ions. For example, hydrochloric acid (HCl) dissociates in water as follows: \[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \] - The increase in H⁺ concentration in the solution leads to a decrease in pH, making the solution more acidic. 3. **Why Option B is Correct:** - Since the primary characteristic of acids is their ability to donate protons, option B accurately describes the behavior of an acid in an aqueous solution. The release of H⁺ ions is what defines the acidic nature of the solution. ### Analysis of Other Options: - **Option A: It increases the concentration of hydroxide ions (OH⁻) in the solution.** - This statement is incorrect because acids do not increase the concentration of hydroxide ions. Instead, they increase the concentration of H⁺ ions. In fact, when an acid is added to water, the concentration of OH⁻ ions may decrease due to the neutralization reaction that occurs when H⁺ ions combine with OH⁻ ions to form water (H₂O). - **Option C: It accepts electrons from the solution.** - This statement is misleading. While some acids can act as electron acceptors in certain reactions (particularly in redox reactions), this is not a defining characteristic of acids in the context of aqueous solutions. The primary behavior of acids in water is proton donation, not electron acceptance. - **Option D: It forms a salt when mixed with a base.** - While it is true that acids react with bases to form salts and water (a neutralization reaction), this statement does not describe the behavior of an acid in an aqueous solution by itself. It describes a reaction between an acid and a base, which is not the focus of the question. ### Summary of Key Points: - Acids are defined by their ability to donate protons (H⁺ ions) in aqueous solutions. - The dissociation of acids in water leads to an increase in H⁺ concentration, lowering the pH. - Other options either misrepresent the behavior of acids or describe reactions that are not relevant to the definition of acids in solution. ### Revision Summary: - Acids donate protons (H⁺) in aqueous solutions. - The increase in H⁺ ions results in a lower pH, indicating acidity. - Acids do not increase hydroxide ion concentration; they may decrease it. - The formation of salts occurs during acid-base reactions, not as a standalone behavior of acids.