Carboxylic acids contain carbonyl group but do not show the nucleophilic addition reactions like aldehydes or ketones. Why?

Explanation

Carboxlic acid do not give the characteristic reaction of carbonyl group (C=O) as given by aldehydes and ketons in carbonxylic acids , the carbonyl group is involed in reasonance as follows
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therefore , it is not a free group . But no reasonance is possible in aldehydes and ketons they give the characterstic reactions of the group but no resonance is possible in adehydes and ketons they give the characterstic reactions of the group.