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