Question

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R.

Assertion A: Phenolphthalein is a pH dependent indicator, remains colourless in acidic solution and gives pink colour in basic medium.
Reason R: Phenolphthalein is a weak acid. It doesn’t dissociate in basic medium.
In the light of the above statements, choose the most appropriate answer from the options given below.

• A. Both A and R are true and R is the correct explanation of A
• B. A is true but R is false
• C. Both A and R are true but R is NOT the correct explanation of A
• D. A is false but R is true

Answer 1

The correct option is B A is true but R is false

Phenolphthalein is a pH dependent indicator. It is a weak acid which is colourless in the acidic solution but gives pink colour in basic medium. The pink colour is due to its conjugate form.
$HPh(aq.)$ $\rightleftharpoons$ $H^{+}$ + $P{h}^{-}$ (pink)

Therefore, assertion (A) is true but Reason (R) is false.