(A) Carboxylic acids contain a carbonyl group but do not give characteristic reactions of the carbonyl group. 
(R) Double bond character of C = O bond in carboxylic acids is greatly reduced due to resonance, as compared to that in aldehydes and ketones

Carboxylic acids do not give characteristic reaction of carbonyl group. This is because the lone pairs on oxygen atom attached to hydrogen atom in the -COOH group are involved in resonance thereby making the carbon atom less electrophilic. Hence, carboxylic acids do not give characteristic reaction of carbonyl group.