Answer: 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 \(-SO_{3}H\), -COOH etc.
Thus, we can conclude that the functional group —COOH is found in aldehydes.
