In the title compound, NH4 +C7H4NO4, the cations and anions are situated on twofold rotation axes. The carboxyl and carboxylate groups are thus disordered; this is consistent with the short and strong O—H O hydrogen bond across an inversion centre between these groups in neighbouring anions. Ion pairing, and intermolecular O—H O and N—H O hydrogen bonds contribute to the crystal packing stability.
