AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
An olfactory indicator is a substance whose smell (odour) changes in acidic and basic solutions. Onion (or clove oil/vanilla) can be used as an olfactory indicator.
Source: Acids, Bases and Salts, Chapter 2
The source passages do not explicitly define olfactory indicators, but this is standard CBSE Chapter 2 content. Examiners expect: (1) a definition mentioning change in smell/odour in acid/base, and (2) one example — onion, vanilla, or clove oil are all accepted. Since this is 1 mark, one crisp sentence with the definition and one example is sufficient. Do not write more.