Acid and base indicators Questions in English

(D) The reaction sequence illustrates the synthesis of phenolphthalein.
Phenolphthalein exists in different structural forms depending on the pH of the solution.
In a basic medium,the molecule exists in a quinonoid form,which is pink in colour.
When treated with excess $NaOH$,the molecule undergoes further deprotonation to form the trianion structure (compound '$X$').
This trianion form lacks the extended conjugated system required for visible light absorption in the visible region,making it colourless.

(D) The reaction sequence illustrates the synthesis and structural changes of phenolphthalein in different pH conditions.
Phenolphthalein acts as an acid-base indicator.
In a basic medium,the molecule exists in a quinonoid form,which imparts a pink/red colour.
When excess $NaOH$ is added,the structure undergoes further deprotonation to form the trianion species labeled as '$X$'.
This trianion form of phenolphthalein is colourless because the extended conjugation of the quinonoid system is disrupted.
Therefore,the compound '$X$' is colourless.