Which of the following best describes the principal difference between a strong acid and a weak acid?

• A. A strong acid is always more concentrated than a weak acid.
• B. A strong acid has a higher molecular weight than a weak acid.
• C. A strong acid completely ionizes in aqueous solution, while a weak acid only partially ionizes.
• D. A strong acid contains more oxygen atoms than a weak acid.

Answer: (C)

Verified step by step guidance

1. Understand that the key difference between strong and weak acids lies in their degree of ionization in water, not their concentration, molecular weight, or oxygen content.
2. Recall that a strong acid completely dissociates into its ions in aqueous solution, meaning it releases all of its hydrogen ions (H\+).
3. Recognize that a weak acid only partially dissociates, so only a fraction of its molecules release hydrogen ions in solution.
4. Note that concentration refers to how much acid is present in solution, which is independent of whether the acid is strong or weak.
5. Summarize that the principal difference is the extent of ionization: strong acids ionize 100%, weak acids ionize less than 100%.