Find all the pairs of ions in the following list which cannot exist together (in appreciable concentration) in the same aqueous solution without precipitating. That is, write any combination of the following ions which would form a precipitate, a weak acid, a weak base, or water. [Note: PbCl2 is slightly soluble.]

Fe^3+ H^+ OH^- Na^+ Cl^- Pb^2+ NO3^- Mg^2+