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(D) Phenolphthalein $(HPh)$ is a weak organic acid.In an acidic medium,the equilibrium $HPh \rightleftharpoons H^{+} + Ph^{-}$ shifts to the left due

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$A$ is true but $R$ is false.

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(D) Phenolphthalein $(HPh)$ is a weak organic acid.In an acidic medium,the equilibrium $HPh \rightleftharpoons H^{+} + Ph^{-}$ shifts to the left due to the common ion effect of $H^{+}$ ions,keeping the concentration of the unionized form $(HPh)$ high,which is colourless.In a basic medium,the $OH^{-}$ ions react with $H^{+}$ to form water,shifting the equilibrium to the right. This increases the concentration of the ionized form $(Ph^{-})$,which is pink in colour.Therefore,Assertion $A$ is true,but Reason $R$ is false because phenolphthalein does dissociate in a basic medium.

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