An organic compound containing $ - COOH $ functional group is called
 $ A. $ Aldehyde
 $ B. $ Ketone
 $ C. $ Amide
 $ D. $ Carboxylic acid

Hint: A functional group is defined as an atom or group of atoms within a molecule that has similar chemical properties whenever it appears in various compounds. There are many types of functional group are such as Amide $ \left( { - N{H_2}} \right) $ , Alcohol $ \left( { - OH} \right) $ , Aldehyde $ \left( { - CHO} \right) $ and so on.

Complete step by step answer:
In an organic compound containing $ - COOH $ functional group is called Carboxylic acid. If the $ \left( { - CO} \right) $ functional group are present then it is known as ketone or if $ \left( { - CHO} \right) $ functional group are present is called Aldehyde and $ \left( { - N{H_2}} \right) $ functional group are present is called Amide.
Thus, the correct option is $ D. $

Additional Information
Aldehyde: An aldehyde is a compound containing a functional group with the structure $ - CHO $ consisting of carbonyl center with the carbon atom also bonded to hydrogen and to an alkyl group. The group without the alkyl is the aldehyde group also known as formyl group. Aldehyde can be made by oxidizing primary alcohol.
Ketone: An organic compound containing a carbonyl group $ = C = O $ bonded to two hydrocarbon groups is called ketone. Ketone can be made by oxidizing secondary alcohols. The simplest such compound is acetone
Amide: An organic compound containing a $ - N{H_2} $ functional group is called an Amide. There are three types of amide namely, primary, secondary and tertiary amides.
Carboxylic acid: An organic compound containing a $ - COOH $ functional group is called a carboxylic acid. This can be prepared by oxidation of tertiary alcohol.

Note:
Functional groups make a molecule special deciding on its reactivity and how it interacts with other molecules. Functional helps to determine the following things of a molecule such as its melting and boiling point, the stability of the molecules, the reactivity of the molecules and also the polarity of the molecules.