The acidity of carboxylic acids depends on the electron-withdrawing ability of substituents attached to the carbon chain. Electron-withdrawing groups like halogens stabilize the carboxylate ion through inductive effect, increasing acidity. The order of increasing acidity effect is Ph < I < Br < Cl < F < CN < NO₂ < CF₃. Fluorine is the most electronegative halogen, providing the strongest electron-withdrawing effect. Additionally, the closer the electron-withdrawing group is to the carboxyl group, the stronger the acid. CF₃ group has three fluorine atoms, making it a powerful electron-withdrawing group, whereas CH₃ is electron-donating and decreases acidity.