(a) Define an indicator.
(b) Explain, why a universal indicator is preferred to acid-base indicators.

(a) Indicators are organic compounds that are used to determine the nature (acidic or basic) of a solution. They are added in small quantity to a solution to determine its acidity or alkalinity with the help of change in colour. For example, acids change the colour of blue litmus to red while bases change the colour of red litmus to blue.

(b) Acid‒base indicators help in determining the acidic or basic nature of a solution; however, they do not help in determining the acidic or basic strength of the solution. So, a universal indicator not only determines the acidic or basic nature of the given solution but also shows how strong or weak the acidic or basic solution is. It gives different colours for different pH ranges. Hence, a universal indicator is preferred over acid‒base indicators.