**Correct Option: B** ### Explanation of the Correct Answer The Bronsted-Lowry theory of acids and bases, proposed by Johannes Nicolaus Bronsted and Thomas Martin Lowry in 1923, defines acids and bases based on their ability to donate and accept protons (H⁺ ions). 1. **Definition of Acids and Bases**: - **Acids**: According to the Bronsted-Lowry theory, acids are defined as substances that can donate protons (H⁺ ions) to other substances. When an acid donates a proton, it forms its conjugate base. - **Bases**: Conversely, bases are defined as substances that can accept protons. When a base accepts a proton, it forms its conjugate acid. 2. **Example**: - Consider hydrochloric acid (HCl) in water: - HCl → H⁺ + Cl⁻ - Here, HCl donates a proton (H⁺) and acts as an acid, while Cl⁻ is its conjugate base. - Now consider ammonia (NH₃): - NH₃ + H⁺ → NH₄⁺ - In this case, NH₃ accepts a proton and acts as a base, forming ammonium (NH₄⁺) as its conjugate acid. This fundamental understanding of acids and bases is crucial in many chemical reactions, particularly in acid-base neutralization reactions. ### Why the Other Options are Incorrect **Option A**: "Acids are substances that can accept protons, while bases are substances that can donate protons." - This statement is incorrect because it reverses the definitions of acids and bases according to the Bronsted-Lowry theory. Acids donate protons, while bases accept them. **Option C**: "Acids and bases both increase the concentration of hydroxide ions in solution." - This statement is misleading. While bases do increase the concentration of hydroxide ions (OH⁻) in solution, acids do not; they typically increase the concentration of hydrogen ions (H⁺). Therefore, this option does not accurately describe the characteristics of acids and bases. **Option D**: "Acids and bases are defined solely by their ability to change the color of pH indicators." - This statement is incorrect because it oversimplifies the definitions of acids and bases. While many acids and bases do change the color of pH indicators (due to their effect on the concentration of H⁺ and OH⁻ ions), this is not a defining characteristic according to the Bronsted-Lowry theory. The theory focuses on proton transfer, not color change. ### Summary of Key Points - **Bronsted-Lowry Theory**: Defines acids as proton donors and bases as proton acceptors. - **Acid-Base Reactions**: Involve the transfer of protons between substances. - **Conjugate Pairs**: Each acid has a conjugate base, and each base has a conjugate acid formed after the proton transfer. - **Misconceptions**: Be cautious of definitions that confuse the roles of acids and bases or focus solely on pH indicators. This understanding of the Bronsted-Lowry theory is essential for mastering acid-base chemistry and will aid in solving related problems in your exams.