1. Carbonate   NH4   SO3   NO3   CO3   Hint Half-n-half Clue   2. Bicarbonate or Hydrogen carbonate   OH   HCO3   Cl   SO4   Half-n-half Clue   3. Bisulfate or Hydrogen sulfate   HSO4   Cl   NH4   PO4   Half-n-half Clue   4. Phosphate   I   PO4   NH4   Cl   Half-n-half Clue   5. Nitrate   SO4   NO3   CO3   O   Half-n-half Clue   6. Oxide   O   S   PO4   I   Half-n-half Clue   7. Hydroxide   SO4   HSO3   OH   O   Half-n-half Clue