Which is a strong acid?

**The reasoning** A **strong acid** is one that completely dissociates (breaks apart 100%) into ions when dissolved in water. Hydrochloric acid (HCl) does exactly this: HCl → H⁺ + Cl⁻ (complete dissociation) When HCl hits water, virtually every single molecule splits into hydrogen ions and chloride ions. This complete ionization is what makes it "strong." Other common strong acids you should know: H₂SO₄ (sulfuric), HNO₃ (nitric), HBr, HI. **Why the wrong options tempt you** All the other options are **weak acids** — they only partially dissociate in water: - **Acetic acid** (CH₃COOH, found in vinegar) — only about 1% breaks apart - **Carbonic acid** (H₂CO₃, in soft drinks) — very weak, mostly stays intact - **Citric acid** (in oranges/lemons) — weak despite tasting sour The trap: students confuse "sour taste" or "corrosive" with "strong acid." Lemon juice tastes very sour but contains weak citric acid! **Quick takeaway** Strong ≠ concentrated or sour; strong means **complete ionization** — and you only need to memorize about 6 strong acids (HCl, H₂SO₄, HNO₃, HBr, HI, HClO₄).