Answer: (iv) Only (d) is correct
The change of colour in acid and base depends on the type of indicator.
A substance that can be added to the reaction mixture to indicate the equivalence point of the titration. Coloured indicators are often used to measure pH. These indicators are a different colour in a basic environment than in an acidic environment. Since indicators are chemical compounds that change colour according to the pH of the solution they are put in.
Examples: Litmus paper and Methyl orange.