Which of the following best defines an acid?

• A. A substance that accepts a proton (H+) from another substance
• B. A substance that donates a proton (H+) to another substance
• C. A substance that forms a precipitate in water
• D. A substance that increases the concentration of OH- ions in solution

Answer: (B)

Verified step by step guidance

1. Recall the Brønsted-Lowry definition of acids and bases: an acid is a substance that donates a proton (H+) to another substance, while a base is a substance that accepts a proton (H+).
2. Analyze each option in the problem: the first option describes a substance that accepts a proton, which corresponds to a base, not an acid.
3. The second option states that an acid is a substance that donates a proton (H+) to another substance, which aligns with the Brønsted-Lowry acid definition.
4. The third option mentions forming a precipitate in water, which is unrelated to the definition of acids or bases and instead relates to solubility.
5. The fourth option describes a substance that increases OH- concentration, which characterizes a base, not an acid.