Preliminary tests with dilute H2SO4 (Group A — decomposed by dilute acid):

• $CO3^{2-}$: Brisk effervescence, gas turns lime water milky (CO2)
• S2-: Rotten egg smell (H2S), turns lead acetate paper black
• $SO3^{2-}$: Suffocating smell (SO2), turns acidified K2Cr2O7 green
• NO2-: Brown fumes (NO2 gas)
• CH3COO-: Vinegar smell (acetic acid)

Tests with concentrated H2SO4 (Group B):

• Cl-: White fumes of HCl, turns NH3 rod white (NH4Cl fumes)
• Br-: Brown vapors of Br2
• I-: Violet vapors of I2
• NO3-: Brown fumes; also brown ring test (FeSO4 + conc. H2SO4 → brown ring of [Fe(NO)(H2O)5]2+ at junction)
• $C2O4^{2-}$: Effervescence with MnO4- (decolorizes KMnO4)

Confirmatory tests:

• $SO4^{2-}$: Add BaCl2 → white BaSO4 precipitate INSOLUBLE in concentrated HCl (this distinguishes from BaSO3 which dissolves)
• $PO4^{3-}$: Add ammonium molybdate + HNO3 → canary yellow precipitate of ammonium phosphomolybdate
• Cl-: AgNO3 → white AgCl soluble in NH3
• Br-: AgNO3 → pale yellow AgBr partially soluble; or CS2 layer test with Cl2 water → orange CS2 layer
• I-: AgNO3 → yellow AgI insoluble; or starch turns blue with I2