Weak acids and bases are indicators. All indicators are weak acids. An acid-base conjugate pair has different colors. Any indicator changes color when the pH of its solution is 7.

What are not acid-base indicators?

Which of the following is not an acid-base indicator? (a) blue litmus (b) methyl orange (c) phenolphthalein (d) Digene. Which of the following is not an acid-base indicator? Digene is not an acid–base indicator but an antacid (base). It is used as a medicine to reduce acidity of the stomach by neutralising it.

How does an indicator differentiate between an acid and base?

Answer: An acid turns blue litmus paper red. A base turns red litmus paper blue. ... Substances which change their smell when mixed with acid or base are known as olfactory indicators.