An aqueous salt solution containing two metal ions was treated with excess cold NaOH solution. A white ppt was obtained which slowly turned to brown (P). To the filtrate (Q) obtained from the above solution hydrochloric acid is added drop-wise. A white ppt was formed first which re-dissolved in excess of $HC\mathcal{l}$  . The brown residue in the filter paper gave a pink colour when strong oxidizing agents like $Pb{O}_2/HN{O}_3$   or sodium bismuthate is added.