question_answer 15)

Consider the following statements : (i) Both acids and bases change colour of all indicators. (ii) If an indicator gives a colour change with an acid, it does not give a change with a base. (iii) If an indicator changes colour with a base, it does not change colour with an acid. (iv) Change of colour with an acid and a base depends on the type of the indicator. Which of the above statements is/are correct? (a) Only (iv) (b) (i) and (iv) (c) (ii) and (iii) (d) All of these  

Answer:

(a) Only (iv) All indicators do not change colour with acids as well as bases, e.g. turmeric changes its colour to pink with base but it remains yellow with acid. Therefore, statement (i) is incorrect. There are some indicators which changes colour with both acid and base, e.g. methyl orange, litmus, thus statement (ii) and (iii) are also incorrect. Statement (iv) is the correct conclusion about indicators.