Which one of the following is the correct seence of change in colours when a turmeric stain on white clothes is scrubbed by soap and then washed with water?

Turmeric is a natural pH indicator containing curcumin, which remains yellow in acidic or neutral environments but changes color in alkaline conditions [1]. A turmeric stain on white clothes is initially yellow. When scrubbed with soap, which is basic (alkaline) in nature, the curcumin undergoes a chemical structural change, turning the stain reddish-brown or deep red [1]. This color change confirms the basic nature of the soap. When the cloth is subsequently washed with plenty of water, the soap is rinsed away, reducing the alkalinity and returning the pH toward neutral. Consequently, the indicator reverts to its original state, and the stain turns yellow again [1]. Therefore, the correct sequence of color change is yellow to reddish-brown and back to yellow.

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 2: Exploring Substances: Acidic, Basic, and Neutral > Table 2.4: Testing the nature of samples with turmeric paper > p. 15