The correct option is **C. Acids react with metals to produce hydrogen gas.** ### Detailed Explanation: 1. **Understanding Acids:** - Acids are substances that can donate protons (H⁺ ions) in a solution. They typically have a sour taste, can conduct electricity, and can react with various substances, including metals. 2. **Analyzing Option C:** - **Acids react with metals to produce hydrogen gas.** This statement is true. When an acid reacts with a metal, a chemical reaction occurs that often produces hydrogen gas and a salt. For example, when hydrochloric acid (HCl) reacts with zinc (Zn), the reaction can be represented as: \[ \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \uparrow \] - In this reaction, zinc displaces hydrogen from hydrochloric acid, resulting in the formation of zinc chloride and the release of hydrogen gas (indicated by the upward arrow). 3. **Why the Other Options are Incorrect:** - **Option A: Acids have a slippery feel and bitter taste.** - This statement is incorrect. Acids do not have a slippery feel; that property is characteristic of bases. Bases feel slippery due to their ability to react with oils and fats, forming soap-like substances. Additionally, acids typically have a sour taste, not a bitter one. Bitter taste is associated with bases. - **Option B: Acids turn litmus paper blue.** - This statement is also incorrect. Acids turn blue litmus paper red. The litmus test is a common method to determine whether a solution is acidic or basic. When an acid is present, it donates protons, which causes the blue litmus paper to change color to red, indicating acidity. - **Option D: Acids are always neutral in pH.** - This statement is false. Acids are characterized by having a pH less than 7. A neutral pH is 7, which is the pH of pure water. Acids, by definition, have a higher concentration of H⁺ ions, resulting in a lower pH value. ### Summary of Key Points: - Acids react with metals to produce hydrogen gas, which is a defining characteristic of their behavior. - Acids have a sour taste and turn blue litmus paper red, not blue. - Acids do not have a slippery feel; that is a property of bases. - Acids are not neutral; they have a pH less than 7. ### Revision Summary: - Acids donate protons (H⁺) and have a sour taste. - They react with metals to produce hydrogen gas. - Acids turn blue litmus paper red. - Acids have a pH less than 7, indicating they are not neutral.