A white shirt has a yellow stain of curry. When soap is rubbed on this shirt during washing, the yellow stain turns reddish-brown. On rinsing the shirt with plenty of water , the reddish- brown stain turns yellow again. (a) Name the natural indicator present in curry stain. (b) Explain the change in colour of this indicator which takes place during washing and rinsing the shirt. What is the nature of soap(acidic/basic) as shown by the indicator present in the curry?