After being given an unknown, you perform the following tests to determine the identity of the cations in solution:

- The addition of NaOH produces a vapor.

- The addition of HCl produces a white precipitate

- The addition of buffered NH4+/NH3 does not produce a precipitate.

- A flame test produced no color

- The addition of ammonium oxalate produced no precipitate

- The addition of strong base produces a precipitate

- After adding a strong base, the resulting solution does not react with a solution of K4Fe(CN)6

Below is the list of the ten ions we studied for the qualitative analysis experiment:

Na+, NH4+, Ag+, Fe3+, Al3+, Cr3+, Ca2+, Mg2+, Ni2+, Zn2+