As written, the card may suggest that S2- is only soluble with Na+, K+, NH4+. This omits information in another card {{c2::S2-}} is {{c1::insoluble}} except with {{c3::Na+}}, {{c3::K+}}, {{c3::NH4+}}, {{c3::Mg2+}}, {{c3::Ca2+}}, {{c3::Sr2+}}, and {{c3::Ba2+}} (Anki id: Anki id: 1559882178075) which is correct according to sigma aldrich's solubility rules (https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/materials-science-and-engineering/solid-state-synthesis/solubility-rules-solubility-of-common-ionic-compounds?srsltid=AfmBOor1rH44bYY6Yjop3ovZx32vO36MZ3SABNk6MFy7S2qYK0g69cNB). It is true that PO4 CO3 S and SO3 share that they are soluble in Na+, K+, and NH4+ but there's no reason to create this grouping with S2- at the expense of creating ambiguity regarding its solubility. This updated group of PO4, CO3, and SO3 alone is favorable because they are exclusively insoluble except with Na+, K+, NH4+ according to sigma Aldrich.