Which solution is appropriate to use in a salt bridge?

Question

Of the compounds NaOH, CuS, and NaNO3, which one is appropriate to use in a salt bridge? Briefly explain your answer, and for each of the other comounds, include a reason why it is not appropriate.

Okay, so I said that NaNO3 is appropriate to use as a salt bridge, because it is an electrolyte solution whose ions will not react with other ions in the cell. Is this right?
I don't know why the other ones wouldn't be appropriate, though.

Answer 1

CuS is extremely insoluble, and NaOH will cause most metal ions in solution to precipitate as their hydroxides.