Question

The following list contains some common polyatomic ions. Using the charge on these ions and the idea of valence, predict the formulas for the following.
nitrate NO3 - phosphate PO4³-
sulfate SO4²- acetate C2H3O2 -
ammonium NH4 4 chromate CrO4²-
carbonate CO3²- dichromate Cr2O7²-
permanganate MnO4 - sulfide S²-
sodium carbonate
potassium permanganate

Answer 1

Sodium carbonate - chemical formula:  Na2CO3
- water-soluble sodium salt of carbonic acid with alkalinizing property
- also known as Disodium carbonate or Carbonic acid disodium salt
 
potassium permanganate - chemical formula:  KMnO4
- inorganic chemical compound and is used for medication
- purplish colored crystalline solid
- noncombustible but accelerates the burning of combustible materials

Answer 2

Answer: $Na_2CO_3$ or Sodium carbonate.

              $KMnO_4$ or Potassium permanganate

Sodium ion carries 1 + charge whereas carbonate ion carries overall charge of -2. So for every carbonate ion, two sodium ions combine to balance the charges and thus form a stable compound, $Na_2CO_3$

Potassium ion carries 1 + charge where as permanganate ion carries overall charge of -1. So for every permanganate ion, one potassium ion combines to balance the charges and thus form a stable compound,  $KMnO_4$

The predicted formulas are shown in the attached image.