JEE MAIN - Chemistry (2022 - 26th July Evening Shift - No. 12)
Given below are two statements: one is labelled as Assertion $$\mathbf{A}$$ and the other is labelled as Reason $$\mathbf{R}$$.
Assertion A: Phenolphthalein is a $$\mathrm{pH}$$ 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.
Both $$\mathbf{A}$$ and $$\mathbf{R}$$ are true and $$\mathbf{R}$$ is the correct explanation of $$\mathbf{A}$$.
Both $$\mathbf{A}$$ and $$\mathbf{R}$$ are true but $$\mathbf{R}$$ is NOT the correct explanation of $$\mathbf{A}$$.
A is true but R is false.
A is false but R is true.
Explanation
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. Therefore,
assertion (A) is true but Reason (R) is false.
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