Question

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 in an acid and a base depends on the type of the indicator.
Which of these statements are correct? [1 mark]

(a) All four
(b) (i) and (iv)
(c) (ii), (iii) and (iv)
(d) Only (iv)

Answer 1

Option (d), Only (iv) [1 mark]

The change in colour of an indicator in an acid and a base depends on the type of indicator. Therefore statement (iv) is correct.

Some indicators, such as litmus and china rose, change colours in both acidic and basic solutions whereas some indicators change colours in either acidic or basic solutions, but not in both cases.

Indicator	Colour in acidic medium	Colour in basic medium
Phenolphthalein	Remains colourless	Pink
Turmeric	Remains yellow	Red
Litmus	Red	Blue
China rose	Pink	Green

From the above table, we can conclude that, statements (i), (ii) and (iii) are not always correct.

Therefore, the correct option is (d).