P−aminobenzenesulfonic acid (sulfanilic acid) is normally written in the form shown but its zwitterionic form is more stable. write a structural formula for the zwitterion.

Zwitterion is an ion consists of equal positive and negative charges on the same molecule which make it more stable and has high melting point 
p-aminobenzene sulfonic acid contains both acidic (-SO₃H) and basic groups (NH₂), the acidic group will lose one proton to give (-SO₃⁻) and the basic group will gain this proton to give (-NH₃⁺)
The structure is:
 

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