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NCERT Solutions Curiosity Chapter 2 –16Fascinating Facts, the Guru Purnima greeting card and olfactory indicators — In-text Questions

Book page 15 Updated on2026-09-05

Q1.
Why is turmeric known as a ‘Golden’ spice?
Answer

Because of its bright golden-yellow colour and the value it has long been given in Indian homes and in Ayurveda.

  • Turmeric is a member of the ginger family, grown in India and other countries.
  • Beyond the taste and colour it gives to food, it is being researched for other benefits.
  • In the Ayurvedic system of medicine it is considered to have numerous health benefits and is used in many traditional home remedies.
And for this chapter: the very pigment that makes turmeric golden is what makes it an indicator. Golden-yellow in acid and neutral liquids, red in a base — the colour is both its identity and its scientific use.
Q2.
Ashwin created a greeting card to pay gratitude to his teacher on the day of Guru Purnima. He applied turmeric paste on white paper and dried it. He wrote his wishes in the teacher's mother tongue (Odia language) on the dried paper using one of the solutions tested in Table 2.4. Which solution can be used to write the message?
Answer

Any basic solution from Table 2.4 — soap solution is the easiest, and baking soda solution, lime water or washing powder solution would work just as well.

Yellow turmeric paper + basic solution
→ the wet letters turn red
→ a red message on a golden background
Why only a base works: turmeric changes colour in a basic medium alone. Writing with lemon juice or vinegar would leave no mark at all, since acids do not affect turmeric — and writing with plain water or sugar solution would leave nothing either.
Try This: make one yourself for a birthday. Brush turmeric paste on a sheet, dry it, then write with a cotton bud dipped in soap solution. The message appears in red as you write, like invisible ink in reverse.
Q3.
Are there any substances whose odours change on adding acidic or basic substances?
Answer

Yes. Substances whose odour changes in an acidic or basic medium are called olfactory indicators.

  • Onion — the sharp onion smell on a cloth strip is strongly reduced by a basic solution such as baking soda solution, while an acidic solution such as tamarind water leaves it much as it was.
  • Vanilla essence and clove oil behave the same way — their characteristic smell disappears in a base.
Why they are useful: a colour indicator is no help to a person who cannot see the colour, or in a dark room. An olfactory indicator gives the answer through the nose instead of the eye — the very idea used in Question 5 of the exercise, where Manya is blindfolded.
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