Question

Arrange the following in increasing order of their $p{K}_a$ values.
(x)
(y)
(z) $C{H}_3-OH$

• A. y < x < z
• B. x < y < z
• C. y < z < x
• D. x < z < y

Answer 1

The correct option is B x < y < z

Strong acid has lesser $p{K}_a$ value.

Carboxylic acid group are more acidic than alcohol group due to the presence of the resonance stabilization.
Thus, compound 'z' is the least acidic compound. Therefore, it has the highest $p{K}_a$ value.
Comparison of 'x' and 'y'
Here compound 'x' has three equivalent resonace stabilising structure whereas compound 'y' has only two equivalent resonance stabilising structure. More the number of equilivalent resonating structure, more will be the stability of conjugate base.
Therefore, compound 'z' is the most acidic compound and has least $p{K}_a$ value.


So acidic strength order is x > y > z
Hence, the increasing order of $p{K}_a$ value is
x < y < z