The term strong and weak acids is used to indicate the

Step 1: Analyze the question The question asks what the terms "strong" and "weak" tell us about an acid.

Step 2: Explain the concept The strength of an acid depends on how completely it ionizes (dissociates) in water.

• Strong acids ionize almost completely in water, producing a large concentration of H⁺ ions. Examples: HCl, HNO₃, H₂SO₄. HCl → H⁺ + Cl⁻ (essentially 100% ionization)
• Weak acids ionize only partially, so most of the molecules stay un-ionized. Examples: ethanoic acid (CH₃COOH), carbonic acid (H₂CO₃). CH₃COOH ⇌ H⁺ + CH₃COO⁻ (only a small fraction ionizes)

Step 3: Evaluate each option

• A. Number of H⁺ released by an acid: This describes basicity of an acid (monobasic, dibasic, tribasic), not its strength. For example, H₂SO₄ is dibasic and H₃PO₄ is tribasic, but H₃PO₄ is a weak acid. ✘
• B. Number of OH⁻ released by an acid: Acids do not release OH⁻ ions. ✘
• C. Extent of ionization of an acid: This is correct. Strong means highly ionized, weak means partially ionized. ✔
• D. Strength of its action on substances: This is vague and not the scientific definition. Even a dilute strong acid and a concentrated weak acid can behave differently, so reactivity is not what defines the term. ✘

Step 4: Answer The correct option is C. extent of ionization of an acid.

Exam tip: Don't confuse strength with concentration.

• Strength is about the extent of ionization (strong or weak).
• Concentration is about how much acid is dissolved (dilute or concentrated).
• Basicity is about the number of replaceable H⁺ (mono-, di-, tribasic).

You can remember it as: Strong = Splits fully, Weak = Wanders partly.