What you have written is gibberish.Na is sodium, a metal. Co is cobalt, a metal. These are very different metals. In this context the 3 is meaningless.If perhaps you meant CO3 (captal O) that is carbonate: C is carbon, O is oxygen, and the 3 means three of the oxygen atoms are bound to the one carbon atom.If you meant NaCO3 this is a nonexistent compound of the metal sodium with carbonate.Na2CO3 is the compound sodium carbonate (washing soda), with two sodium atoms bound to one carbonate.NaHCO3 is the compound sodium bicarbonate (baking soda), with one sodium atom and one hydrogen atom bound to one carbonate.