Describe in each case what you could add to the following aqueous solutions in order to separate one or more cations or anions in NaNO3 and Ba(NO3)2?

Your question isn't exactly clear. We can add Na2SO4 to the aqueous mixture and ppt BaSO4, filter and dry; however, we don't have Ba(NO3)2 anymore. However, that will separate the Ba^+2 from the mixture. I don't know if that is suitable or not.