Q1. [1] § 2.1 UNDERSTANDING THE CHEMICAL PROPERTIES OF ACIDS AND BASES § 2.2 WHAT DO ALL ACIDS AND ALL BASES HAVE IN COMMON? § 2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS?
Which one of the following can be used as an acid-base indicator by a visually impaired (blind) student ?
- A Turmeric
- B Vanilla essence
- C Methyl orange
- D Litmus
Previously asked in CBSE board exam
2026 31/1/1 Q18
Generated by claude-sonnet-4-6 · 2026-06-15 06:42 · grounding rag
Model Answer
Answer: B — Vanilla essence
Vanilla essence is an olfactory indicator — its odour changes in acidic/basic media, making it suitable for visually impaired students who cannot detect colour changes.
Explanation
- Visually impaired students cannot observe colour changes, so visual indicators (turmeric, methyl orange, litmus) are not useful for them.
- Olfactory indicators work by change in smell, not colour. The textbook (Activity 2.2) identifies vanilla essence as one such olfactory indicator — its characteristic odour is lost in a basic (NaOH) solution but retained in an acidic one.
- Onion and clove oil are also olfactory indicators mentioned in the chapter, but vanilla essence is the one given in the options.
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