Arrange in decreasing order of acidity: (I) ethanoic acid, (II) phenol, (III) cyclohexanol.

A $III > II > I$
B $II > I > III$
C $I > II > III$
D $I > III > II$

Answer: C

The conjugate base of ethanoic acid (acetate) has the charge shared equally by two oxygens. Phenoxide shares it with the ring carbons, a weaker delocalisation, and cyclohexoxide has no delocalisation. The approximate pKa values are 4.8, 10 and 16, giving I > II > III.

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Arrange in decreasing order of acidity: (I) ethanoic acid, (II) phenol, (III) cyclohexanol.

Answer: C

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