Which of the following exists as a zwitter ion ?

Step-by-step solution

Sulfanilic acid (p-aminobenzenesulfonic acid) contains both an acidic group ( -SO₃H ) and a basic group ( -NH₂ ). The strongly acidic sulfonic acid group donates a proton to the basic amino group, resulting in the formation of an internal salt or a dipolar ion known as a zwitterion. The structure of the zwitterion is p - ^+H₃N-C₆H₄-SO₃^- . The other given compounds do not possess a combination of a sufficiently strong acidic group and a basic group to form a stable zwitterion. Answer: Sulfanilic acid