Indicators change the colour of substances according to its acidic or basic nature.For example, china rose indicators turns acidic solutions to dark pink and basic solutions to green.How is this possible?

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Solution

In solutions, the indicators are present in two forms, HIn and In^-. and these two forms have distinct colours. Now, in solution there are two reactions which can occur, depending on whether an acid or a base is added in the solution.
If acid is added to the solution, more HIn is present and this changes the color of the solution as per the form HIn.
If base is added, more In^- is present, which changes the color of the solution to that of In^-.

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Q58) Consider the following statements about acid-base indicators.

i) Phenolphthalein gives a pink colour if the solution is acidic.

ii) China rose indicator turns acidic solutions to dark pink.

iii) Blue litmus turns red for a basic solution.

Which of the above statements are true?

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