The correct option is **B. Acids turn blue litmus paper red and have a sour taste.** ### Detailed Explanation: 1. **Understanding Acids:** - Acids are substances that can donate protons (H⁺ ions) in a solution. They are characterized by their ability to produce hydrogen ions when dissolved in water. - Common examples of acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and acetic acid (CH₃COOH). 2. **Litmus Test:** - Litmus paper is a pH indicator used to test whether a solution is acidic or basic. Blue litmus paper turns red in the presence of an acid. - This color change occurs because the hydrogen ions from the acid interact with the dye in the litmus paper, causing a change in color. 3. **Taste of Acids:** - Acids are known for their sour taste. For example, citric acid in lemons and acetic acid in vinegar are both acids that have a distinctly sour flavor. - This property is often used in culinary applications, where acids can enhance the flavor of food. 4. **Why Option B is Correct:** - Option B accurately describes two well-known properties of acids: their ability to turn blue litmus paper red and their sour taste. These properties are fundamental characteristics of acids and are widely recognized in chemistry. ### Why the Other Options are Incorrect: - **Option A: Acids have a slippery feel and can conduct electricity.** - **Incorrect because:** While acids can conduct electricity due to the presence of ions in solution, they do not have a slippery feel. The slippery feel is characteristic of bases (alkalis), which produce slippery solutions due to the formation of soap-like substances when they react with fats and oils. - **Option C: Acids react with metals to produce hydroxide ions.** - **Incorrect because:** Acids react with metals to produce hydrogen gas (H₂) and a salt, not hydroxide ions (OH⁻). For example, when zinc reacts with hydrochloric acid, it produces zinc chloride and hydrogen gas: \[ \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \] - Hydroxide ions are produced by bases, not acids. - **Option D: Acids are always neutral and do not affect the pH of solutions.** - **Incorrect because:** Acids are not neutral; they lower the pH of a solution. A neutral solution has a pH of 7, while acidic solutions have a pH less than 7. The presence of hydrogen ions from acids is what causes the solution to be acidic. ### Summary of Key Points: - Acids turn blue litmus paper red and have a sour taste. - They donate protons (H⁺ ions) in solution, affecting pH. - Acids react with metals to produce hydrogen gas, not hydroxide ions. - Bases, not acids, have a slippery feel and can produce hydroxide ions. This understanding of acids and their properties is crucial for mastering the fundamentals of chemistry and preparing for professional exams.