AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
The H⁺(aq) ion (hydronium ion, H₃O⁺) is responsible for the acidic nature of a solution. Acids produce H⁺ ions in aqueous solution, which give them their acidic properties.
Source: Chapter 2, Section 2.2
The examiner expects you to name H⁺(aq) or H₃O⁺ as the ion responsible. Either notation is acceptable, but mentioning both shows thorough understanding. The parallel fact — that OH⁻(aq) is responsible for basic nature — is often asked alongside, so keep it in mind.