The ascending order of acidity of $$-OH$$ group in the following compounds is : 

(A) Bu-OH

Choose the correct answer from the options given below :

• (A) Bu-OH (Butanol): An aliphatic alcohol. Lacks resonance stabilization for its conjugate base, making it the least acidic in the group.
• (C) 4-Methoxyphenol: The $$-\text{OCH}_3$$ group at the para-position exerts a strong electron-donating mesomeric ($$+M$$) effect, which destabilizes the phenoxide ion. It is less acidic than unsubstituted phenol.
• (D) Phenol: Standard reference with resonance-stabilized phenoxide ion.
• (B) 4-Nitrophenol: The $$-\text{NO}_2$$ group at the para-position acts as a strong electron-withdrawing group ($$-M, -I$$), strongly stabilizing the negative charge.
• (E) 2,4-Dinitrophenol: Contains two strong electron-withdrawing nitro groups ($$-\text{NO}_2$$) stabilizing the phenoxide ion via resonance and induction, making it the most acidic.

Final Ascending Order:

$$\text{(A)} < \text{(C)} < \text{(D)} < \text{(B)} < \text{(E)}$$