Carboxyl. The carboxyl functional group is often referred to as an acid group because it is very acidic.

Which functional groups are the most acidic?

The carboxylate is resonance stabilised to a very significant extent, as the negative charge on oxygen is delocalised extensively between 2 electronegative oxygens. This makes the carboxylate very stable, hence carboxylic acid is the most acidic functional group.

How do you know if a functional group is acidic or basic?

The functional group helps to determine whether something is acid, low pH, or basic and has a high pH. An example of an acidic functional group is a carboxyl. The carboxyl functional group is acidic because it is a proton (H+) donator when in solution.