The functional group —cooh is found in
(1) esters (3) alcohols
(2) aldehydes (4) organic acids

Option (2) is the correct answer.

Explanation:

When for a particular compound a group of atoms shows certain characteristics reactions then that group is known as functional group.

Functional group of esters is "-COO".

Functional group of alcohols is "-OH".

Functional group of aldehydes is "-COOH".

Organic acids are the compounds that show acidic properties. Like , -COOH etc.

Thus, we can conclude that the functional group —COOH is found in aldehydes.