Arrange the following in the decreasing order: ClCH₂COOH, Cl₃CCOOH, CH₃COOH, Cl₂CHCOOH

The greater the number of electron-withdrawing substituents, the greater the dispersal of the negative charge and hence stronger will be the acid. Hence, the order of acidity is

Cl₃CCOOH > Cl₂CHCOOH > ClCH₂COOH > CH₃COOH

Strength of carboxylic acids

Carboxylic acids are weak acids because they only partially ionise in solution. Their solutions do not contain many hydrogen ions than a strong acid solution at the same concentration. Acetic acid is ten times weaker than formic acid confirming the electron-donating character of an alkyl group relative to hydrogen.