The correct order of decreasing acidity of the following aliphatic acids is:

The acidity of carboxylic acids is influenced by the inductive effect of alkyl groups. Alkyl groups are electron-donating (+I effect).As the size and number of alkyl groups attached to the carboxyl group increase, the +I effect increases.This increase in electron density toward the carboxylate ion destabilizes the conjugate base, thereby decreasing the acidity.$\text{HCOOH}$ (no alkyl group) is the strongest acid.${\text{CH}}_3\text{COOH}$ (one methyl group) is weaker.$({\text{CH}}_3{)}_2\text{CHCOOH}$ (isopropyl group) is still weaker.$({\text{CH}}_3{)}_3\text{CCOOH}$ (tert-butyl group) is the weakest.Order: $\text{HCOOH}>{\text{CH}}_3\text{COOH}>({\text{CH}}_3{)}_2\text{CHCOOH}>({\text{CH}}_3{)}_3\text{CCOOH}$.