Ans. There are several types of indicators, including litmus paper, phenolphthalein, bromothymol blue, methyl orange, and universal indicator. Litmus paper is a simple indicator that turns red in acidic solutions and blue in basic solutions. Phenolphthalein is colorless in acidic solutions and turns pink in basic solutions. Bromothymol blue is yellow in acidic solutions, green in neutral solutions, and blue in basic solutions. Methyl orange is red in acidic solutions and yellow in basic solutions. Universal indicator is a mixture of several indicators and can display a range of colors to indicate the pH of a solution.