What colour does the turmeric paper turn when put in an alkaline solution?

16 What is an indicator? Name three common indicators. 16 Name the acid-base indicator extracted from lichen. 17 What is an olfactory indicator? Name two olfactory indicators. What is the effect of adding sodium hydroxide solution to these olfactory indicators? 18 What happens when an acid reacts with a metal? Give chemical equation of the reaction involved.