Arrange the following compounds in increasing order of their acid strengths:

A. o-Cresol, pK_a = 10.2

B. m-Nitrophenol, pK_a = 8.3

C. Phenol, pK_a = 10

Choose the correct answer from the options given below:

A, C, B

Since the pK_a is the negative logarithmic value of Ka, pK_a is a smaller value for strong acid.

Lower the pK_a vlaue, the stronger the acid is. Similarly, higher the pK_a value, the weaker the acid is.

By looking at the pKa values of different acids, one can compare the relative acid strengths.

A. o-Cresol, pK_a = 10.2 (least acidic)

B. m-Nitrophenol, pK_a = 8.3 (most acidic)

C. Phenol, pK_a = 10

Increasing acidic strength: A < C < B

In substituted phenols, the presence of electron withdrawing groups such as nitro group, enhances the acidic strength of phenol.

On the other hand, electron releasing groups, such as alkyl groups, in general, do not favour the formation of phenoxide ion resulting in decrease in acid strength. Cresols, for example, are less acidic than phenol.