$word_{count}$: 200

Group A — Decomposed by dilute H2SO4: $CO3^{2-}$ → brisk effervescence, gas turns lime water milky (CO2). S2- → rotten egg smell (H2S), blackens lead acetate paper. $SO3^{2-}$ → suffocating smell (SO2), turns acidified K2Cr2O7 green. NO2- → brown fumes (NO2). CH3COO- → vinegar smell (CH3COOH). Group B — Decomposed by conc. H2SO4: Cl- → white HCl fumes (turns NH3 rod white). Br- → brown Br2 vapors. I- → violet I2 vapors. NO3- → brown fumes; brown ring test with FeSO4 + conc. H2SO4. Confirmatory tests: $SO4^{2-}$ → BaCl2 → white BaSO4 INSOLUBLE in conc. HCl. $PO4^{3-}$ → ammonium molybdate + HNO3 → canary yellow precipitate. Cl- → AgNO3 → white AgCl soluble in NH3. Br- → AgNO3 → pale yellow; or CS2 layer turns orange with Cl2 water. I- → AgNO3 → yellow; or starch turns blue with I2. $C2O4^{2-}$ → decolorizes KMnO4; CaCl2 → white CaC2O4. Key distinctions: BaSO4 vs BaCO3 (acid solubility), AgCl vs AgBr vs AgI (color + NH3 solubility).