What is a strong acid?

• A. An acid that completely ionises giving H+ ions in solution.
• B. An acid that partially ionises in solution.
• C. An acid that does not ionise in water.
• D. An acid that neutralises bases immediately.

Answer: (A)

A strong acid is one that completely dissociates in water, producing a large concentration of H+ (hydronium) ions. This full ionisation means the solution has many charge carriers, so it conducts electricity well. In contrast, a weak acid only partially ionises in solution, so there are fewer H+ ions at equilibrium. The rate at which an acid reacts with bases isn’t what defines its strength; a strong acid’s defining feature is its tendency to dissociate completely in water. An acid that does not ionise in water wouldn’t behave as an acid in the usual sense.