you can have one, more than one, or none.
choosing from S_2, SO_3, SO_4, CO_3, NO_3, Br, I, Cl, and PO_4. after adding HNO_3 and AgNO_3 to part of the unknown a black precipitate forms. to a fresh solution of the unknown you add NH_3 and BaCl_2. a ppt forms you save both the supernatant and ppt. to the ppt you add HCl and the formation of bubbles is noticed. to the same precipitate you add H2O and more HCl and centrifuge. you then save the supernatant and ppt and divide the supernatant into two tubes. after adding bromine water to the first tube saved with supernatant you get a white ppt. after adding a molybate solution to the second supernatant you get a yellow ppt. which ions are present?