Thank you for reporting, we will resolve it shortly
Q.
Most acidic is:
BHUBHU 2003
Solution:
$H ^{+}$donors are acids. Electron donating groups increase acidity and electron withdrawing groups decrease acidity.
In $C H _{3} C O O H$ and $CH _{3} CH _{2} COOH$ : Alkyl groups donate electrons towards O-H group due to $+I$ effect and increases the bond strength of $C - H$ bond.
$\therefore $ Acidity is decreased.
In $C _{6} H _{5} COOH$ : Phenyl group attracts the electrons away from benzene ring and hence, O-H bond strength decreases and therefore acidity increases.
$HCOOH$ : It has neither $+I$ or $-I$ effect. So its acidity is not affected.
$\therefore C _{6} H _{5} COOH$ is most acidic.