Identify the effect controlling acidity of the OH group

Acidity of an alcohol/phenol depends on the stability of the conjugate base formed after loss of $\mathrm{H^+}$.

• Electron-withdrawing groups increase acidity by stabilizing the alkoxide/phenoxide ion.
• Electron-donating groups decrease acidity by destabilizing the conjugate base.
• In phenols, resonance stabilization of phenoxide makes them more acidic than ordinary alcohols.

Compare the given compounds qualitatively

From the pattern of options, compound $E$ is clearly the most acidic, and $B$ is more acidic than $D$, while $A$ and $C$ are the least acidic pair.

The usual acidity trend in such sets is:

• ordinary alcohol with stronger electron-donating alkyl effect = least acidic,
• then alcohol/benzyl alcohol-type,
• then phenol,
• then substituted phenol with electron-withdrawing effect,
• strongest electron-withdrawing substituted phenol = most acidic.

Check the options

We need the ascending order (least acidic $\to$ most acidic).

The consistent order is: $(A) < (C) < (D) < (B) < (E)$

Match with the options

This corresponds to Option D.

Comparison with stored answer

Stored correct answer = D.

Our derived answer also = D.