Asolution containing a mixture of metal cations was treated as follows. 1. dilute hcl was added and a precipitate formed. the precipitate was filtered off. 2. h2s was bubbled through the acidic solution. again, a precipitate formed and was filtered off. 3. the ph was raised to about 9 and h2s was again bubbled through the solution. no precipitate formed. 4. finally, sodium carbonate was added and no precipitate formed. what can be said about the presence of each of these groups of cations in the original solution?