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 a

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:

Canvas Classes · Accepted Answer

Step 1 — Evaluate Assertion A:

Phenolphthalein:
- In acidic medium (pH < 8.3): exists as  (colourless lactone form) ✓
- In basic medium (pH  10): exists as  (pink quinonoid form) ✓
- It is indeed pH-dependent

Assertion A is TRUE ✓

Step 2 — Evaluate Reason R:

Phenolphthalein IS a weak acid — this part is correct.

However, the statement "It doesn't dissociate in basic medium" is INCORRECT. In basic medium, phenolphthalein dissociates (loses protons) to form the coloured  ion:

The pink colou

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