Which of the following statements about universal indicator is/are true?
- 1It is a mixture of several indicators.
- 2It shows different colours at different concentrations of hydrogen ions in solution.
- 3It helps to determine the strength of given acid and base in titration.
Select the correct answer using the code given below:
- A1 only
- B1 and 2 only
- C2 and 3 only
- D1, 2 and 3
Explanation
A universal indicator is a blend of several pH indicators (such as thymol blue, methyl red, bromothymol blue and phenolphthalein), so statement 1 is true. The blend displays a continuous spectrum of colours as the hydrogen-ion concentration changes, so statement 2 is true and it reports approximate pH. On the paper's intended reading, that pH indication 'helps' compare the relative strength of an acid or base during titration, so statement 3 is counted true. Key disputed: some reputable keys mark B (1 and 2 only), arguing that a universal indicator's gradual colour change cannot fix a sharp titration end-point the way phenolphthalein or methyl orange can.