Statement I : The pH range of any indicator is from pKIn – 1 to pKIn + 1Statement II : The pH of indicator is given as, pH=pKln+logln-[Hln]. Colour change of indicator takes place when ln-=[Hln]

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Statement I and II are correct

Statement I is correct and Statement II is incorrect

Statement - I is incorrect and Statement II is correct

Both statement - I and statement - II are False

answer is B.

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Detailed Solution

Any indicator is characterised by the characteristic color of its ionised or non-ionised formHIn Colorless ⇌H++In- Colored After equivalents point, the system is a buffer containing the weak acid HIn and its conjugate In-. PH of a such a system is given PH=PKaHIn+logIn-[HIn]At equivalents point no color is observed and so [HIn] = 10 x [In-]At the end point, color is observed properly and so [In-] = 10[HIn]Thus when PH=PKIn+log110=PKIn - 1system is colorless and when PH=PKIn+log10=PKIn +1system is colored therefore, range of PH for a color change is PKIn -1 to PKIn +1An average human eye can recognize a color when the concentration of the colored form is roughly 10 times that of the colorless form.

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